Add ability to create AtomicString using LChar* buffer and length

Add ability to create AtomicString using LChar* buffer and length
https://bugs.webkit.org/show_bug.cgi?id=94381

Reviewed by Geoffrey Garen.

Allows the use of 8 bit string data directly without converting to 16 bits first.

* wtf/text/AtomicString.cpp:
(WTF::LCharBufferTranslator::hash):
(LCharBufferTranslator):
(WTF::LCharBufferTranslator::equal):
(WTF::LCharBufferTranslator::translate):
(WTF::AtomicString::add):
* wtf/text/AtomicString.h:
(WTF::AtomicString::AtomicString):
(AtomicString):
* wtf/text/StringImpl.h:
(StringImpl):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@125958 268f45cc-cd09-0410-ab3c-d52691b4dbfc