Use new clang_getFileContents to efficiently convert
utf8 byte offsets from line start to column numbers.
Also provide simplier backwards convertion to pass
resulting utf8 offset to clang.
Task-number: QTCREATORBUG-16941
Change-Id: If0e58fe01ad3e281b7e952e972b9e86f6e75aadb
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>
Now it's in accordance with clangrefactoringbackend/source and
clangpchmanagerbackend/source.
Change-Id: I939cfc72cffb8fcde0649f125e6efb6670d1cbc3
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>