CSS Selectors Level 4: enable case-insensitive attribute matching by default

CSS Selectors Level 4: enable case-insensitive attribute matching by default
https://bugs.webkit.org/show_bug.cgi?id=142960

Reviewed by Andreas Kling.

Source/WebCore:

All open issues have been resolved, enable the feature by default.

Test: fast/css/attribute-selector-case-insensitive.html

* css/CSSGrammar.y.in:

LayoutTests:

This test is imported from blink. That's the only test
they have for this feature.

* fast/css/attribute-selector-case-insensitive-expected.txt: Added.
* fast/css/attribute-selector-case-insensitive.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@181900 268f45cc-cd09-0410-ab3c-d52691b4dbfc