CDD: Update requirements for app compatibility in Q.

- Update definition of non-SDK interfaces (previously hidden APIs) to
  reflect the name used in other docs. Update the definition of what
  they are based on AOSP changes in Q.
- Update definition of API classifications, as per code changes in Q.
- Add signed config requirement (new feature in Q), and remove the optional
  dynamic update since that is no longer needed.

Patched from http://ag/6933982

Bug: 122980592
Test: N/A
Change-Id: Ia74f196f8ecb228337cebe8977daa5492117551e

• 3_software/3_1_managed-api-compatibility.md[diff]