Provides apps the rounded corners info

- Created a new @hide class RoundedCorners
  - The class is used to create and manager all the rounded corners.
- Created a new public class RoundedCorner
  - Represent each rounded corner.
- Created a new public API in Display to get the original rounded
  corners.
- Created a new public API in WindowInsets to get the rounded corners
  relative to the window bounds.

Bug: 161808676
Test: atest RoundedCornerTest RoundedCornersTest
      DisplayPolicyLayoutTests DisplayPolicyTests
      WallpaperControllerTests
Change-Id: I58c671b0e9a077cdf26764c6302537c72db0f667