[clang-rename] speedup RenamingAction

The complexity of renaming a USR is O(N) [N stands for number of nodes in
Translation Unit]. In some cases there are more than one USR for a single symbol
(see overridden functions and ctor/dtor handling), which means that the
complexity of finding all of the corresponding USRs is O(N * M) [M stands for
number of USRs corresponding to the symbols, which may be not quite small]. With
a simple tweak we can make it O(N * log(M)) by passing whole list of USRs
corresponding to the symbol to USRLocFinder.

llvm-svn: 277131