Add SET_CLIP_SOURCE permission.

This adds a permission that allows the holder to provide the source
package when setting the primary clip in clipboard. This will be done
using a new system API.

This is needed to ensure that the clipboard access notifications can be
properly attributed. For example, when a copy is performed through the
share sheet, the data should be attributed to the app that opened the
share sheet, not Android System.

Bug: 180577866
Test: builds
Change-Id: If3193d476fa923b849b505ad8b6dd893a2feae8f