Fixes #22342

Summary

This PR adds support for suggesting names when typing incomplete tuple elements in method bodies. Previously, name suggestions only worked when the tuple syntax was fully formed.

Problem

When typing an incomplete tuple like this:

void M()
{
    (List<Person> 
}

The IDE would not suggest "people" as a name for the tuple element, even though it worked correctly for complete tuples:

void M()
{
    (List<Person> , int i)  // ✅ Suggests "people" for first element
}

Root Cause

The C# parser creates different syntax nodes depending on how complete the tuple is:

• Complete tuple: (List<Person> , int i) → TupleExpressionSyntax (handled by IsTupleLiteralElement)
• Incomplete tuple: (List<Person> → ParenthesizedExpressionSyntax (not handled)
• Tuple in parameter: void M((List<Person> ) → TupleTypeSyntax (handled by IsTupleTypeElement)

Solution

Added a new method IsIncompleteParenthesizedTuple to DeclarationNameInfo.cs that detects when the user is typing an incomplete tuple by:

1. Checking if the cursor is inside a ParenthesizedExpressionSyntax
2. Verifying the expression inside the parentheses resolves to a type symbol
3. Returning the appropriate NameDeclarationInfo for name generation

The implementation follows the same pattern as existing tuple handling methods and is placed appropriately in the check chain.

Testing

Added ten test cases covering:

• Generic types: (List<Person> $$ → suggests "people"
• Predefined types: (int $$ → suggests "i"
• Qualified names: (System.Action $$ → suggests "action"
• Fully qualified generic types: (System.Collections.Generic.List<Person> $$ → suggests "people"
• Array types: (Person[] $$ → suggests "people"
• Variants with closing paren present for all of the above

All builds successful with no regressions expected.

Fixes #75347

Fixes #75347

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