"Rename symbol under cursor" allows symbols to be renamed to reserved words

If a user calls "Rename symbol under cursor" on a function name and changes it to a C++ reserve keyword, such as `register` or `typedef`, Qt Creator replaces the symbol name with the reserved word on all files.

How to reproduce:

• declare function foo()
• call "Rename symbol under cursor" on function
• rename function to a reserved word such as `register` or `typedef` or `const`

It would be nice if Qt Creator validated the input string to avoid renaming symbols to reserved words.