[Mfill Android] Create adapter for accessory bridge

By creating an adapter between autofill popup controller and keyboard
accessory bridge, we can change the mapping of autofill suggestion
positions without special-casing every function in the controller.

Before this CL, the mapping logic was in the bridge code where it did
not belong.

Other advantages of this CL:
 * Fully unit-tested
 * Doesn't use two loops and a mapping array for the job of an int.

Bug: None
Change-Id: I049db975f8b2afe11f55360abab6640f52a92080
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1533943
Commit-Queue: Friedrich [CET] <[email protected]>
Reviewed-by: Vasilii Sukhanov <[email protected]>
Cr-Commit-Position: refs/heads/master@{#646723}
11 files changed