Semi-fix bug #10013 (CSS Quick Edit provider does not respond if project contains any non-UTF8 CSS/LESS/SCSS files)

Semi-fix for bug #10013 -- Silently ignore files that can't be read, and continue the search anyway (warning logged to console, but no user-visible error shown). Similar to what we've always done for Find in Files.

With unit test, and matching test for the pre-existing same behavior in Find in Files. Also clean up dated use of `waitsFor()` in the CSSUtils test spec.
I added the extra newlines in this file for better section differentiation, since it's almost 3000 lines long and quite hard to navigate.  Ideally we should eventually split it up into multiple smaller test suites.  If people strongly disagree with the added spacing I can take it back out, but otherwise I think this is an improvement in the meantime while the suite is still large.