Rename WallpaperColorExtractor to WallpaperLocalColorExtractor

The new class name is more accurate: this class extracts color for
specified areas of the wallpaper.

Bug: 243402530
Test: atest ImageWallpaperTest
Test: atest WallpaperLocalColorExtractorTest
Change-Id: I1cae6a3c93e2ce852256d9826ca5a6146964cc32
3 files changed