Adjust Color Provider to handle consecutive calls

Color Provider needs to be able to handle consecutive calls because
there are 2 section controllers collecting from the color flow on the
main page. To do so, wallpaper color loading is made synchronous, and
the colors are stored once loaded, so that they can be re-used if there
are no wallpaper color changes.

Flag: NONE
Bug: 326293722
Test: manually verified that wallpaper color options display in both
home and lock color sections and the color picker fragment
Test: regression tested color picker features including pausing and
resuming app and changing light/dark theme, no regressions observed

Change-Id: I2bd7b958b8959dfbd77e5d62da3b0fec75bd4169