Add missing lock guards on Terminal access (#15894)

`Terminal` is used concurrently by at least 4 threads. The table
below lists the class members and the threads that access them
to the best of my knowledge. Where:
* UI: UI Thread
* BG: Background worker threads (`winrt::resume_background`)
* RD: Render thread
* VT: VT connection thread

|                                    | UI | BG | RD | VT |
|------------------------------------|----|----|----|----|
| `_pfnWriteInput`                   | x  | x  |    | x  |
| `_pfnWarningBell`                  |    |    |    | x  |
| `_pfnTitleChanged`                 |    |    |    | x  |
| `_pfnCopyToClipboard`              |    |    |    | x  |
| `_pfnScrollPositionChanged`        | x  | x  |    | x  |
| `_pfnCursorPositionChanged`        |    |    |    | x  |
| `_pfnTaskbarProgressChanged`       |    |    |    | x  |
| `_pfnShowWindowChanged`            |    |    |    | x  |
| `_pfnPlayMidiNote`                 |    |    |    | x  |
| `_pfnCompletionsChanged`           |    |    |    | x  |
| `_renderSettings`                  | x  |    | x  | x  |
| `_stateMachine`                    | x  |    |    | x  |
| `_terminalInput`                   | x  |    |    | x  |
| `_title`                           | x  |    | x  | x  |
| `_startingTitle`                   | x  |    | x  |    |
| `_startingTabColor`                | x  |    |    |    |
| `_defaultCursorShape`              | x  |    |    | x  |
| `_systemMode`                      |    | x  | x  | x  |
| `_snapOnInput`                     | x  | x  |    |    |
| `_altGrAliasing`                   | x  |    |    |    |
| `_suppressApplicationTitle`        | x  |    |    | x  |
| `_trimBlockSelection`              | x  |    |    |    |
| `_autoMarkPrompts`                 | x  |    |    |    |
| `_taskbarState`                    | x  |    |    | x  |
| `_taskbarProgress`                 | x  |    |    | x  |
| `_workingDirectory`                | x  |    |    | x  |
| `_fontInfo`                        | x  |    | x  |    |
| `_selection`                       | x  | x  | x  | x  |
| `_blockSelection`                  | x  | x  | x  |    |
| `_wordDelimiters`                  | x  | x  |    |    |
| `_multiClickSelectionMode`         | x  | x  | x  |    |
| `_selectionMode`                   | x  | x  | x  |    |
| `_selectionIsTargetingUrl`         | x  | x  | x  |    |
| `_selectionEndpoint`               | x  | x  | x  |    |
| `_anchorInactiveSelectionEndpoint` | x  | x  | x  |    |
| `_mainBuffer`                      | x  | x  | x  | x  |
| `_altBuffer`                       | x  | x  | x  | x  |
| `_mutableViewport`                 | x  |    | x  | x  |
| `_scrollbackLines`                 | x  |    |    |    |
| `_detectURLs`                      | x  |    |    |    |
| `_altBufferSize`                   | x  | x  | x  | x  |
| `_deferredResize`                  | x  |    |    | x  |
| `_scrollOffset`                    | x  | x  | x  | x  |
| `_patternIntervalTree`             | x  | x  | x  | x  |
| `_lastKeyEventCodes`               | x  |    |    |    |
| `_currentPromptState`              | x  |    |    | x  |

Only 7 members are specific to one thread and don't require locking.
All other members require some for of locking to be safe for use.

To address the issue this changeset adds `LockForReading/LockForWriting`
calls everywhere `_terminal` is accessed in `ControlCore/HwndTerminal`.
Additionally, to ensure these issues don't pop up anymore, it adds to
all `Terminal` functions a debug assertion that the lock is being held.

Finally, because this changeset started off rather modest, it contains
changes that I initially made without being aware about the extent of
the issue. It simplifies the access around `_patternIntervalTree` by
making `_InvalidatePatternTree()` directly use that member.
Furthermore, it simplifies `_terminal->SetCursorOn(!IsCursorOn())` to
`BlinkCursor()`, allowing the code to be shared with `HwndTerminal`.

Ideally `Terminal` should not be that much of a class so that we don't
need such coarse locking. Splitting out selection and rendering state
should allow deduplicating code with conhost and use finer locking.

Closes #9617

## Validation Steps Performed
I tried to use as many Windows Terminal features as I could and fixed
every occurrence of `_assertLocked()` failures.

src/cascadia/TerminalCore/terminalrenderdata.cpp

@@ -29,11 +29,13 @@ const TextBuffer& Terminal::GetTextBuffer() const noexcept
 
 const FontInfo& Terminal::GetFontInfo() const noexcept
 {
+    _assertLocked();
     return _fontInfo;
 }
 
 void Terminal::SetFontInfo(const FontInfo& fontInfo)
 {
+    _assertLocked();
     _fontInfo = fontInfo;
 }
 
@@ -105,6 +107,8 @@ const std::wstring Microsoft::Terminal::Core::Terminal::GetHyperlinkCustomId(uin
 // - The pattern IDs of the location
 const std::vector<size_t> Terminal::GetPatternId(const til::point location) const
 {
+    _assertLocked();
+
     // Look through our interval tree for this location
     const auto intervals = _patternIntervalTree.findOverlapping({ location.x + 1, location.y }, location);
     if (intervals.size() == 0)
@@ -125,7 +129,7 @@ const std::vector<size_t> Terminal::GetPatternId(const til::point location) cons
 
 std::pair<COLORREF, COLORREF> Terminal::GetAttributeColors(const TextAttribute& attr) const noexcept
 {
-    return _renderSettings.GetAttributeColors(attr);
+    return GetRenderSettings().GetAttributeColors(attr);
 }
 
 std::vector<Microsoft::Console::Types::Viewport> Terminal::GetSelectionRects() noexcept
@@ -185,19 +189,14 @@ void Terminal::SelectNewRegion(const til::point coordStart, const til::point coo
 }
 
 const std::wstring_view Terminal::GetConsoleTitle() const noexcept
-try
 {
+    _assertLocked();
     if (_title.has_value())
     {
-        return _title.value();
+        return *_title;
     }
     return _startingTitle;
 }
-catch (...)
-{
-    LOG_CAUGHT_EXCEPTION();
-    return {};
-}
 
 // Method Description:
 // - Lock the terminal for reading the contents of the buffer. Ensures that the
@@ -223,5 +222,6 @@ const bool Terminal::IsUiaDataInitialized() const noexcept
     // when a screen reader requests it. However, the terminal might not be fully
     // initialized yet. So we use this to check if any crucial components of
     // UiaData are not yet initialized.
+    _assertLocked();
     return !!_mainBuffer;
 }