JavaScript extension: argument-name parsing and untested paths #5355

Describe the problem
Two gaps in JavaScript extensions (jsextension and initialize_js_extension), found while working on #5352 and #5354.

1. Argument names are probably parsed wrongly for some function shapes. Node takes the text between the first ( and the next ) of fn.toString() with /\((.*?)\)/ (extractArgumentsStringFromJavascript in node/playwright-wrapper/playwright-state.ts), and Python splits it on , and = (Browser._jskeyword_call). Likely wrong:

• a single parameter without parentheses: exports.f = x => ...
• a default that contains , or ): function f(a = [1, 2]), function f(a = g())
• destructuring: function f({ selector, timeout })
• a default that is a bare identifier: function f(t = DEFAULT) raises NameError when the keyword is generated, instead of DataError

None of these has a test. The fix might be to report unsupported shapes clearly rather than to parse them.

2. Paths without a unit test. They work today and some are exercised by acceptance tests, but nothing at the unit level stops them from changing silently:

• logger messages reaching the Robot Framework log (response.log -> logger.info)
• fn.rfdoc becoming the keyword documentation, and the "TODO: Add rfdoc string" text used without one
• the generated keyword's @keyword name
• Could not find keyword <name> for an unknown function name
• initializeExtension in Node: no Jest test

3. LibraryComponent.call_js_keyword clashes on an argument named keyword_name. #5354 made keyword_name positional-only in Browser.call_js_keyword, but the plugin wrapper in Browser/base/librarycomponent.py still has it as an ordinary parameter. A plugin calling self.call_js_keyword("lookUp", keyword_name="Click") for function lookUp(keyword_name) gets TypeError: call_js_keyword() got multiple values for argument 'keyword_name'. Make it positional-only too.

Where tests go
Python: utest/test_js_extension_call.py has a recording gRPC stub for the generated keyword and call_js_keyword. Node: node/playwright-wrapper/__tests__/playwright-state.test.ts already tests extensionKeywordCall.