Fixes #21889

* 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

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.

CR feedback.

"replace" is roughly allowed in the same contexts as "async", so the "replace" ecommender is basically a copy of "async" recommender.

Fixes: https://github.com/dotnet/roslyn/issues/11191

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.