Add <extension-sdk> manifest tag inside <uses-sdk>

This allows apps to specify the minimum versions they need
of extension sdks, and fails install if they aren't met.

There is additional work required to prevent local rollbacks
from triggering a downgrade of SDK versions after an install.

Bug: 137191822
Test: atest PackageParserTest
Exempt-From-Owner-Approval: PS4 was approved
Change-Id: If61ae6c67ceb752bec6876006a29e52b996901e7