[refactor] add clang-refactor tool with initial testing support and


[refactor] add clang-refactor tool with initial testing support and
local-rename action

This commit introduces the clang-refactor tool alongside the local-rename action
which uses the existing renaming engine used by clang-rename. The tool
doesn't actually perform the source transformations yet, it just provides
testing support. This commit also moves only one test from clang-rename over to
test/Refactor. I will continue to move the other tests throughout
development of clang-refactor.

The following options are supported by clang-refactor:

-v: use verbose output
-selection: The source range that corresponds to the portion of the source
that's selected (currently only special command test:<file> is supported).

Please note that a follow-up commit will migrate clang-refactor to
libTooling's common option parser, so clang-refactor will be able to use
the common interface with compilation database and options like -p, -extra-arg,

The testing support provided by clang-refactor is described below:

When -selection=test:<file> is given, clang-refactor will parse the selection
commands from that file. The selection commands are grouped and the specified
refactoring action invoked by the tool. Each command in a group is expected to
produce an identical result. The precise syntax for the selection commands is
described in a comment in TestSupport.h.

Differential Revision: https://reviews.llvm.org/D36574