* Rename Foo to Goo

* Rename ifoo to igoo

* Add back BOMs

* Parse ref/readonly-ref extension methods

* Address PR Comments

* Fix break

* More PR Comments

* Fix break

Fixes #16565

* Combine deconstruction assignment and declaration, and support discards.

- Combine deconstruction assignment and declaration, and support discards.
- Add wildcards.work.md to track outstanding work.
- Bind each type syntax once in a deconstruction.
- Because tuples may contain declarations, adjust lambda disambiguation
  and adjust parsing of argument lists.
- Diagnose tuple element names on the left of a deconstruction.
- Add relational operators to disambiguating tokens in 7.5.4.2

* Disallow deconstruction declarations except at the statement level.
This is now a semantic restriction (until we decide to remove it).

* Revise logic to detect `var` in a declaration expression.
Plus other changes per code review.

* Add a test that GetTypeInfo on a discard expression doesn't crash.
* Small changes per code review.
* Add (skipped) test for var invocation in parens.
* Rename "Discarded" to "Discard"
* Changes recommended via code review.
* Minor changes to the handling of declaration expressions per code review.
* Addressing blocking feedback while Neal is OOF

Fixes https://github.com/dotnet/roslyn/issues/14794
Fixes https://github.com/dotnet/roslyn/issues/14832

This PR implements completion for the simple cases of async and void in
a local function context. What it misses cases where parsing incorrectly
considers bare modifiers to be local variable declaration statements
rather than local function declaration statements. This is tracked by
bug #14525.

Fixes #8616
Fixes #8617

Suggest types (and intrinsic type keywords) after "(" when declaring a tuple type as the type of a member.

Fixes #14127

Similarly for TupleDeconstructionVariableDesignation.
Also found many places to handle both kinds of foreach statements.

Apply feedback from Pilchie
Apply feedback from CyrusNajmabadi
Missed feedback from CyrusNajmabadi
Apply more feedback from CyrusNajmabadi and AlekseyTs
Apply feedback from AlekseyTs
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Adjust implementation of SyntaxTreeExtensions.IsLocalVariableDeclarationContext around Out Variable Declarations.

Fixes #12121.

Adjusted behavior of CSharpSyntaxGenerator and added some explicitly written code to achieve the following for the Syntax Model:
- Factory static ArgumentSyntax Argument(NameColonSyntax nameColon, SyntaxToken refOrOutKeyword, CSharpSyntaxNode expressionOrDeclaration) will be internal.
- Factory static ArgumentSyntax Argument(CSharpSyntaxNode expressionOrDeclaration) will be internal.
- There will be the following public factories:
public static ArgumentSyntax Argument(NameColonSyntax nameColon, SyntaxToken refOrOutKeyword, ExpressionSyntax expression)
public static ArgumentSyntax Argument(ExpressionSyntax expression)
public static ArgumentSyntax Argument(NameColonSyntax nameColon, SyntaxToken outKeyword, VariableDeclarationSyntax declaration)
public static ArgumentSyntax Argument(SyntaxToken outKeyword, VariableDeclarationSyntax declaration)
- Update method ArgumentSyntax Update(NameColonSyntax nameColon, SyntaxToken refOrOutKeyword, CSharpSyntaxNode expressionOrDeclaration) will be internal.
- There will be the following public update methods:
public ArgumentSyntax Update(NameColonSyntax nameColon, SyntaxToken refOrOutKeyword, ExpressionSyntax expression)
public ArgumentSyntax Update(NameColonSyntax nameColon, SyntaxToken outKeyword, VariableDeclarationSyntax declaration)
- With method ArgumentSyntax WithExpressionOrDeclaration(CSharpSyntaxNode expressionOrDeclaration) will be internal.
- There will be the following public With methods:
public ArgumentSyntax WithNameColon(NameColonSyntax nameColon)
public ArgumentSyntax WithRefOrOutKeyword(SyntaxToken refOrOutKeyword)
public ArgumentSyntax WithExpression(ExpressionSyntax expression)
public ArgumentSyntax WithDeclaration(VariableDeclarationSyntax declaration)
- Property CSharpSyntaxNode ExpressionOrDeclaration will be internal.
- Instead there will be the following public properties (one of them will return null depending on the value of ExpressionOrDeclaration):
public ExpressionSyntax Expression
public VariableDeclarationSyntax Declaration
- Factory, Update and With methods should provide stronger validation:
a) ExpressionOrDeclaration must either be an ExpressionSyntax, or a VariableDeclarationSyntax;
b) Declaration must be combined with out keyword;
c) Declaration must have single VariableDeclarator;
d) VariableDeclarator must have null ArgumentList and null Initializer.

Note: we have to conservatively assume that parenthesized expression could also be a tuple in progress.

Improves comments around the IsCompleteSubmission.
Throws argument exception when the syntax is not a submission.
Uses the Parser.CheckFeatureAvailability to check multiline strings.
Renames the IsScriptOrInteractive to IsScript.
Handle incomplete members such as an annotation.
Do not show completions when inside of a directive.
Add tests for symbol completion provider.