Allow ShortcutInfo to specify a theme for splash screen.(5/N)

Provides new APIs so that shortcuts can preset the theme of the splash
screen window.
- Static way: android:splashScreenTheme
  Preset the splash screen theme from xml.
- Dynamic way: ShortcutInfo.Builder#setStartingTheme
  Preset the splash screen theme when construct the ShortcutInfo
  programmatically.

Bug: 73289295
Test: build/flash
Test: atest AppWindowTokenTests ActivityRecordTests
Change-Id: Ie5e73f9b22fea22659e496c12198c942f4bc93cd