Update signature files to the new format

The new format is described in tools/metalava/FORMAT.md.

Change-Id: I91820fa3c0de39ac95b523d7d7fafd7fb7ecc50a
Fixes: 116589402 Switch signature files over to the v2 format
Fixes: 112626813 Drop "synchronized" modifier from the signature format
Fixes: 122358225 Omit overriding methods that only differ in final [...]
Fixes: 73088715 API Review: Need doclava to output nullability
Fixes: 79739773 API Review: Metalava enforcing constants are constant
Exempt-From-Owner-Approval: Large-scale tooling change
Test: make sdk, make update-api, make checkapi
Merged-In: I2172319e3d580eb4b1ffc43616e5595dba20f026
6 files changed