Prevent infinite loop in unstable AST JSDoc scanner

[Copilot]

The unstable AST JSDoc scanner could loop indefinitely when a scan range ended immediately after -, because the range check did not guard the full identifier condition.

Changes

• Guard both identifier parts and hyphens with pos < end:

while (pos < end && (isIdentifierPart(...) || char === CharacterCodes.minus))

• Add regression coverage verifying that a range ending in x- reaches EOF and preserves the expected tokens.

• Fixes unstable/ast: scanJsDocToken infinite-loops when a scan range ends on a trailing '-' (fix from #63581 not carried into the AST scanner) #64135