Organize typemaps in //mojo/ shared for Blink variant

BUG=

Change-Id: Ie397047eb79a8639d5e14718f076c17376f9a252
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1619204
Reviewed-by: Ken Rockot <rockot@google.com>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Leon Han <leon.han@intel.com>
Cr-Commit-Position: refs/heads/master@{#661602}
4 files changed