Clarify semantics in call composer extras

Docs updates:
* setCallExtraParcelable must take a framework-defined parcelable
* EXTRA_PICTURE_URI takes an android.net.Uri
* Remove redundant documentation on setCallComposerStatus

Fixes: 182510687
Test: docs only
Change-Id: I43f776cf8bcb72c4121515536a3790cf44bf1638