Delegate window decor view binding / updating to *ViewHolders

Moves view binding and updates from the new task data in relayout
to a *ViewHolder class made for each "type" of window decoration UI.
This allows caching of findViewById calls and isolated view binding
logic for different UI variants of the caption window decoration.

Bug: 269618335
Test: use proto1/proto2 and switch between modes, no UI/behavior
changes observed

Change-Id: Ib2f1d194af72883653ac93bbd98ae4e9e7b4376a