Add a Compatibility and Terminal page to the Settings UI (#17895)

## Summary of the Pull Request
Adds a global Compatibility page to the settings UI. This page exposes
several existing settings and introduces a few new settings:
- compatibility.allowHeadless
- compatibility.isolatedMode
- compatibility.textMeasurement
- debugFeatures

This also adds a Terminal subpage for profiles in the settings UI. This
page includes:
- suppressApplicationTitle
- compatibility.input.forceVT
- compatibility.allowDECRQCRA
- answerbackMessage

Several smaller changes were accomplished as a part of this PR:
- `experimental.input.forceVT` was renamed to
`compatibility.input.forceVT`
- introduced the `compatibility.allowDECRQCRA` setting
- updated the schema for these new settings and
`compatibility.allowHeadless` (which was missing)
- add `Feature_DebugModeUI` feature flag to control if debug features
should be shown in the SUI

Verified accessible via Accessibility Insights

A part of #10000
Closes #16672

doc/cascadia/profiles.schema.json

@@ -2355,11 +2355,21 @@
           "description": "When set to true, the terminal will focus the pane on mouse hover.",
           "type": "boolean"
         },
+        "compatibility.allowHeadless": {
+          "default": false,
+          "description": "When set to true, Windows Terminal will run in the background. This allows globalSummon and quakeMode actions to work even when no windows are open.",
+          "type": "boolean"
+        },
         "compatibility.isolatedMode": {
           "default": false,
           "description": "When set to true, Terminal windows will not be able to interact with each other (including global hotkeys, tab drag/drop, running commandlines in existing windows, etc.). This is a compatibility escape hatch for users who are running into certain windowing issues.",
           "type": "boolean"
         },
+        "compatibility.allowDECRQCRA": {
+          "default": false,
+          "description": "When set to true, the terminal will support the DECRQCRA (Request Checksum of Rectangular Area) escape sequence.",
+          "type": "boolean"
+        },
         "copyFormatting": {
           "default": true,
           "description": "When set to `true`, the color and font formatting of selected text is also copied to your clipboard. When set to `false`, only plain text is copied to your clipboard. An array of specific formats can also be used. Supported array values include `html` and `rtf`. Plain text is always copied.",