style: Move the error reporter into ParserContext.

Summary:
This should make it easier to report errors, and also reduce codesize.

The reason this was so generic is that error reporting was unconditionally
enabled and was super-hot, but now that's no longer the case after bug 1452143,
so we can afford the virtual call in the "error reporting enabled" case.

This opens the possibility of simplifying a lot the error setup as well, though
this patch doesn't do it.

Test Plan: No behavior change, so no new tests.

Reviewers: xidorn

Bug #: 1469957

Differential Revision: https://phabricator.services.mozilla.com/D1734

MozReview-Commit-ID: F3wTdhX9MB5

components/style/properties/properties.mako.rs

@@ -1442,6 +1442,7 @@ impl UnparsedValue {
                 None,
                 ParsingMode::DEFAULT,
                 quirks_mode,
+                None,
             );
 
             let mut input = ParserInput::new(&css);