[2/n] Add cache to width/height thin definition

Convertion between dp and pixel just need to be done
when density changes. We implemented an IntSupplier
which returns a cached value updating only when
density changes.

Bug: 334077350
Bug: 339738650
Test: atest WmTests:LetterboxConfigurationTest

Change-Id: I7adb6cd94d9f1908ea15561a1654914cb3665e19