tofu: Context.Validate now takes a context.Context

This continues our ongoing effort to get a coherent chain of
context.Context all the way from "package main" to all of our calls to
external components.

Context.Validate doesn't yet do anything with its new context, but we'll
plumb this deeper in future.

Since the local backend's implementation of backend.Local.LocalRun calls
Validate on the given configuration before returning, it this also extends
that interface method to take a context, and so the various commands that
directly create "local runs" (rather than going through the backend
operation API) now all pass in a context derived from the one created
in "package main".

All of the _test.go file updates here are purely mechanical additions of
the extra argument. No test is materially modified by this change, which
is intentional to get some assurance that isn't a breaking change.

Signed-off-by: Martin Atkins <mart@degeneration.co.uk>

internal/backend/remote/backend_context.go

@@ -23,7 +23,9 @@ import (
 )
 
 // Context implements backend.Local.
-func (b *Remote) LocalRun(op *backend.Operation) (*backend.LocalRun, statemgr.Full, tfdiags.Diagnostics) {
+//
+//nolint:funlen,nestif // Historical function predates our complexity rules
+func (b *Remote) LocalRun(_ context.Context, op *backend.Operation) (*backend.LocalRun, statemgr.Full, tfdiags.Diagnostics) {
 	var diags tfdiags.Diagnostics
 	ret := &backend.LocalRun{
 		PlanOpts: &tofu.PlanOpts{