Fix blurred app icon on resize veil.

When we create the bitmap for the icon, we specify the size as the same
size as app header icon. Create 2 different bitmaps for resize veil and
the app header icon.

Test: atest DesktopModeWindowDecorationTests
Test: Manually check that resize veil icon is not pixelated
Bug: 339506623
Change-Id: I35283ee0b4156c10b140eedc78d40512b8a37d70