Use JSDoc directly in syntactic classifier rather than reparsing

[jakebailey]

Fixes #47537

This is an alternative to #52710 which instead solves the issue by not reparsing the JSDoc, instead using the JSDoc that's already parsed in the tree.

Perhaps this is unwise, as:

• I don't know who actually uses this classifier anymore.
• If we skip parsing in TS files in the future, we'll not classify these at all. (Skip parsing JSDoc in .ts files #52466 ish) This is wrong; we are definitely going to be parsing JSDoc in services for editor features.
• It doesn't address the (very real) bugs exposed/fixed in Ensure that JSDoc parsing happens within a ParsingContext #52710.
• Maybe this only works because we don't have enough test coverage for putting comments into strange places.

[jakebailey]

Turns out I was confused, this is the syntactic classifier and not the semantic classifier, so it's not "old". But, VS Code doesn't use this thing, so, I'm still not sure who does.

[DanielRosenwasser]

Unfortunately substr allocates so:

Suggested change

	const text = sourceFile.text.substr(start, 3);
	if (text === "/**") {
	const sourceText = sourceFile.text;
	if (start + 3 <= sourceText.length && sourceText.charCodeAt(start) === CharacterCodes.slash
	&& sourceText.charCodeAt(start + 1) === CharacterCodes.asterisk && sourceText.charCodeAt(start + 2) === CharacterCodes.asterisk) {

[jakebailey]

I think this is the wrong fix anyway; please review #52710 instead.