Allow delimiter defaults in optional JSDoc parameters

[Pybsama]

Summary

• allow single-token delimiter default values in bracketed optional JSDoc parameters
• preserve the existing interpretation of ] as the closing bracket, including empty defaults such as [name=]
• add regression coverage for parenthesis defaults and the empty-default compatibility case

Root cause

The compatibility parser discarded a JSDoc Toolkit default value only when the lexer classified it as STRING. Parentheses are emitted as distinct tokens, so the parser left them in place and then reported a false missing closing ] warning.

Validation

• bazelisk test //:test/com/google/javascript/jscomp/parsing/JsDocInfoParserTest --test_filter='JsDocInfoParserTest.testUnsupportedJsDocSyntax*' (OK (4 tests))
• bazelisk test //:test/com/google/javascript/jscomp/parsing/JsDocInfoParserTest (OK (780 tests))
• bazelisk test //:all (431 test targets passed)
• git diff --check

Fixes #3767