Move WebKit/common/ mojom files to WebKit/public/mojom (2)

- array_buffer
- clipboard
- color_chooser
- feature_policy

Also renames feature_policy_struct_traits.{h,cc} to
feature_policy_mojom_traits.{h,cc} per the standard mojom
naming guideline.

Did some relevant edits in README.md etc too.

[email protected],[email protected],[email protected]

Bug: 809983
Change-Id: I31a6f7a497423fa0c099d12ba93755bf737e7a76
Reviewed-on: https://chromium-review.googlesource.com/925983
Commit-Queue: Kinuko Yasuda <[email protected]>
Reviewed-by: Kinuko Yasuda <[email protected]>
Cr-Commit-Position: refs/heads/master@{#537754}
59 files changed