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.
@busykai I put breakpoints in the contained tests and they get run with the "CSS Parsing" suite of Integration tests. Were you expecting to see "CSS Intgration Tests" in the list? It's not shown due to the way Jasmine groups the tests.