Support file-local types in EE

[RikkiGibson]

Related to #60819

roslyn/src/ExpressionEvaluator/CSharp/Source/ExpressionCompiler/CompilationContext.cs

Lines 709 to 713 in a540733

	// PROTOTYPE(ft): add tests and adjust implementation to allow EE to access file types
	Binder binder = new BuckStopsHereBinder(compilation, associatedSyntaxTree: null);
	var hasImports = !importRecordGroups.IsDefaultOrEmpty;
	var numImportStringGroups = hasImports ? importRecordGroups.Length : 0;
	var currentStringGroup = numImportStringGroups - 1;

roslyn/src/ExpressionEvaluator/CSharp/Source/ExpressionCompiler/Binders/EEMethodBinder.cs

Lines 47 to 48 in a540733

	// PROTOTYPE(ft): add tests and adjust implementation to allow EE to access file types
	_sourceBinder = new InMethodBinder(substitutedSourceMethod, new BuckStopsHereBinder(next.Compilation, associatedSyntaxTree: null));