Allow DisplayContent to report per-Display minimal task size.

Currently minimal task size is calculated from the default display in
RootWindowContainer and used for all resizeable tasks; instead we should calculate this from per-Display
context to extend for additional displays.

Test: DisplayContentTests
Bug: 191434136

Change-Id: Ib9397de5570c0b17651c4ccfcb30bee836f684e8
8 files changed