[clang-move] Enable dump all declarations in old header.
Summary:
* Add -dump_dels option to dump all declarations from old header. It
will allow clang-move used as a frontend to get declarations from
header. Further more, this will make debugging stuff easier. Currently only
class/function types are supported.
* Refactoring code a little bit by creating a ClangMoveContext which
holds all options for ClangMoveTool, which can simplify the code in
some degree.
Reviewers: ioeric
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D27059
llvm-svn: 287863