Add Tests to ViewCapture Library

I have added some tests to verify the correctness of ViewCapture. Additionally, I have added a Readme with some remarks regarding performance.
In order to make the ViewCapture class better testable, I have modified it such that there are now two getInstance() functions. One of them takes three arguments to tune some parameters for testing.

Bug: 255929005
Test: atest frameworks/libs/systemui/viewcapturelib/tests/com/android/app/viewcapture
Change-Id: I36b72a2cc0aba45ef2af2684ca1487525b9595fc
7 files changed
tree: c57fc82196c99a9794b92afde4a9fb299e0b60e3
  1. iconloaderlib/
  2. searchuilib/
  3. viewcapturelib/