Following https://github.com/angular/angular/pull/64509 we started
choking on unbalanced closing parentheses in declaration blocks,
specifically in quoted background-image urls. This was reported in
https://github.com/angular/angular/issues/65137.
This occured because we previously (and now again) traverse the entire
declaration block when selecting for :host-context() selectors to shim.
This is an oddity of how we parse styles today, and is likely something
we'd want to remove if we parsed selectors properly.
This change adds a new flag to _splitOnTopLevelCommas which allows it to
continue past unbalanced closing parentheses in the declaration block,
returning _convertColonHostContext to its previous behavior while
keeping support for the extra nesting in :host-context().
(cherry picked from commit 9e7ddcaa10)