Move SkTSearch.h into src.

No public headers are using it anymore, so move it from include/private
into src/core where SkTSearch.cpp resides.

Change-Id: I4499c629487ff1b8c391b44708616d67567a3e9b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/213674
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
22 files changed