[lexical-code-prism] Bug Fix: read the language maps as own properties

[luantaraschi]

Description

normalizeCodeLanguage and getLanguageFriendlyName are declared as returning a string, and for a handful of language names they return a function instead.

Both read their map with a plain index, and both maps are object literals:

CODE_LANGUAGE_MAP[lang] || lang
CODE_LANGUAGE_FRIENDLY_NAME_MAP[_lang] || _lang

So a language whose name matches a member of Object.prototype resolves to the inherited value rather than falling through to lang:

normalizeCodeLanguage('constructor')     -> function Object
normalizeCodeLanguage('toString')        -> function toString
normalizeCodeLanguage('valueOf')         -> function valueOf
normalizeCodeLanguage('hasOwnProperty')  -> function hasOwnProperty
normalizeCodeLanguage('__proto__')       -> Object.prototype

The language of a code block is whatever the document carries, so the name is not ours to choose. The markdown transformer reads the info string of a fence and hands it straight to $createCodeNode:

const language = startMatch[2] || undefined;
...
codeBlockNode = $createCodeNode(language);

so importing ```constructor is enough to reach it. From there the playground's CodeActionMenuPlugin renders getLanguageFriendlyName(lang) as the label and passes normalizeCodeLanguage(...) to canBePrettier, both of which now receive a function.

Worth mentioning because it is the thing that convinced me the fix belongs here rather than at the call sites: the sibling facade already gets this right. normalizeCodeLanguage in @lexical/code-shiki looks the name up with bundledLanguagesInfo.find(...), an array search, so no name can reach a prototype member.

I kept both maps as plain objects, since they are exported and swapping them for a Map would be a breaking change for anyone reading or spreading them. The lookups go through a small helper that only accepts own properties, which leaves the || fallback behaving exactly as before for every language that is actually in the map.

Test plan

Two tests added to CodePrismLanguageOptions.test.ts: one walks the six names above through both functions, and one asserts the ordinary mappings still work, so the guard cannot quietly swallow a real language.

Before

The new test fails on the current code:

× returns a string for a language named after an Object member
  AssertionError: expected [Function Object] to be 'constructor'

After

✓ Prism code language options > includes Go (#7704)
✓ Prism code language options > returns a string for a language named after an Object member
✓ Prism code language options > still maps and names the languages it knows

Test Files  1 passed (1)
     Tests  3 passed (3)

The wider suite is unchanged: packages/lexical-code-prism, packages/lexical-code-shiki and packages/lexical-code-core together give 10 files, 213 tests, all passing.

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