Added SyntaxGenerator.AliasImportDeclaration overload that takes a SyntaxNode for the name to create an alias for.

This change ensures that extension methods are only classified specially when declared or when
called in a reduced form. If an extension method is called as an ordinary static method invocation,
it is classified as an oridinary method.

This change renames the recently added `ClassificationTypeNames.EnumFieldName` to
`ClassificationTypeNames.EnumMemberName` to be consistent with other Roslyn APIs (such as EnumMemberDeclarationSyntax).
In addition, the newly added `ClassificationTypeNames` constants for member classification were incorrectly added to
PublicAPI.Shipped.txt rather than PublicAPI.Unshipped.txt. This commit fixes that (since the APIs haven't shipped yet).

Fixes issue #20355?

Is there something special about this bug or am I missing something? There's just an extra space that needs removed, right?

* Fix UseLocalFunction when converting a single-line lambda.

* Add more tests.

* Arrays/pointers/nullables of intrinsic types are intrinsic. Type of array creations is apparent. Handle out vars.

* Use GetOriginalSemanticModel instead of duplicating logic
* Move local function to separate helper method

Fixes #23461