Add ActivityEmbedding Property key

Allow apps to define ActivityEmbedding related flags in AndroidManifest
using <property> tags, so that the system can read the info before the
apps launch.

The property is for apps to provide consent to allow the System to
override ActivityEmbedding rules for the apps.

Bug: 236778622
Test: atest
      CtsWindowManagerJetpackTestCases:ActivityEmbeddingPropertyTests
Change-Id: Ibd5f9ed41b94de0bf9ff2c81a7ffa19d1067b769