Cache window and icon color of splash screen starting window

The background color of splash screen starting window may depend
on the declared window background and the content if icon. That
may be expensive operations if the drawables are not using pure
color. Because the attributes to compute the colors are simple,
it only need a few fields to identify whether the incoming request
has been computed. So it is worth to cache them with very small
extra memory. The cache of a package will be cleared if the package
is removed or replaced.

It may save the creation time up to 20ms (depends on the complexity
of the drawable).

Bug: 190176296
Test: atest StartingSurfaceDrawerTests#testColorCache
Test: Cold/warm launch app twice and compare the duration of
      trace name "makeSplashScreenContentView". The second time
      should be faster. Re-install the app and launch again,
      the trace will contain "peekWindowBGColor" that means
      that cache for the package was cleared.

Change-Id: I61158416694a226999843fa8fc6a8b23d6893f02