Update smallestScreenWidthDp when split bounds resized

Update smallestScreenWidthDp of the splitting tasks, so client apps can
determine which resources they should apply.

Fix: 217600744
Fix: 220069817
Test: atest WMShellUnitTests
Test: manual check smallestScreenWidthDp of splitting apps in winscope

Change-Id: Ie36065a951dfab2d4bb8d7a56dbc12ae03ff4033
7 files changed