Add #setWindowingLayer to ActivityOptions

Adds widowing layer enumeration and AO member to store selected layer.
Javadoc to be provided in separate cl as a subject to api review

Bug: 373303599
Bug: 433413402
Flag: com.android.window.flags.enable_interactive_picture_in_picture
Test: atest ActivityOptionsTest
Change-Id: Ia827166649aa02aa9ec1d9e6925de91caddde5b2