Batch parsing of inline scripts/stylesheets

[MegaCorn]

Before: html5ever produces tokens for each line of inline content
After: html5ever batchs inline contents until encounter '<', which represents endtag in most cases
Fixes: servo/servo#34502

[simonwuelker]

html5ever emits the line number for each token it parses. I this change will break the line counting, because we no longer hit

html5ever/html5ever/src/tokenizer/mod.rs

Lines 258 to 260 in a7c9d98

	if c == '\n' {
	self.current_line.set(self.current_line.get() + 1);
	}

for each newline in the input data. That's probably why we interrupt the tokenizer when we see a newline in the first place.

I'd like to get rid of the line count at some point, because it also has a significant performance overhead in other places (#601 (comment)), but I have not investigated the implications.