Dromaeo tests usage of StringImpl find routines cause 8->16 bit conversions

Dromaeo tests usage of StringImpl find routines cause 8->16 bit conversions
https://bugs.webkit.org/show_bug.cgi?id=76645

Reviewed by Geoffrey Garen.

* wtf/text/StringImpl.cpp:
(WTF::equalIgnoringCase): New LChar version.
(WTF::findInner): New helper function.
(WTF::StringImpl::find): Added 8 bit path.
(WTF::reverseFindInner): New helper funciton.
(WTF::StringImpl::reverseFind): Added 8 bit path.
(WTF::StringImpl::reverseFindIgnoringCase): Added 8 bit path.
* wtf/text/StringImpl.h:
(WTF):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@106019 268f45cc-cd09-0410-ab3c-d52691b4dbfc