Fix signature help ranges to prevent display after closing parentheses

[Copilot]

Signature help was incorrectly being shown for positions after closing parentheses and in whitespace following function calls. For example:

let obj = {
    foo(s: string): string {
        return s;
    }
};

let s = obj.foo("Hello, world!")/*afterCall*/  
  /*afterNewline*/;

Previously, both afterCall and afterNewline positions would incorrectly show signature help for the foo method when they should show none.

Root Cause

The issue was in getContainingArgumentInfo which was finding argument information for KindCloseParenToken nodes even when the cursor position was at or after the end of the closing parenthesis. This caused signature help to be displayed in positions where it shouldn't appear.

Solution

Added logic to skip KindCloseParenToken nodes when the position is at or after their end position:

// Special case: if we're at a close paren token and the position is after its end, 
// don't provide signature help. This handles the case where the cursor is right 
// after the closing parenthesis
if n.Kind == ast.KindCloseParenToken && position >= n.End() {
    continue
}

Testing

• Added TestSignatureHelpRangeIssue that validates signature help is shown inside calls but not after closing parentheses
• Added runSignatureHelpTestWithNil test helper to validate cases where signature help should NOT be provided
• Verified existing signature help functionality still works correctly
• Added TestSignatureHelpNestedCallPrecedence to document a related issue with nested call precedence (to be addressed separately)

Impact

This fix improves the user experience by ensuring signature help only appears in appropriate contexts within function calls, eliminating the confusing behavior where signature help would persist after completing a function call.

Addressing #1419.

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[DanielRosenwasser]

I think the real fix is to implement/port the commented out code:

		// !!!
		// const containingList = findContainingList(startingToken);
		// return !!containingList && contains(invocationChildren, containingList);

[Copilot]

I've implemented the commented-out code as suggested. The fix includes:

1. Proper findContainingList logic for comma tokens with containsNodeList helper function
2. Extended isSyntacticOwner to handle CloseParenToken cases to prevent signature help after closing parentheses
3. Added getASTChildren helper to work with AST structure instead of just tokens
4. Applied syntactic owner checks for critical cases like CloseParenToken even when onlyUseSyntacticOwners is false

The range-based fix has been replaced with this more comprehensive TypeScript-compatible solution in commit 8991cdb.