Adds a hook clang-include-fixer-add-include-hook that is invoked with the path...

Adds a hook clang-include-fixer-add-include-hook that is invoked with the path and type of the added include.

This patch also adds a new function clang-include-fixer-from-symbol, which prompts the user for a symbol to resolve and include.

Patch by Torsten Marek.

llvm-svn: 295814