Enable color resources loader to be created using FRRO

Adjust OverlayManagerImpl to enable creating self-targeting FRRO with
"android" as a target package and without a target overlayable. Then
adjust ColorResources#create to overlay android colors using a
self-targeting FRRO, instead of using ARSC file manipulation.

Flag: EXEMPT bug fix
Bug: 365751758
Test: Manually verified colors are overlaid in Customization Picker
Launcher preview

Change-Id: If3dd47323cd1b2db51e46725399ecd2227405140