Add API signature files for the system server APIs

... so that they can be reviewed.

Bug: 140202860
Test: m

Exempt-From-Owner-Approval: cherry-pick from internal

Merged-In: Iec8cdd30ad5e4979d56140a8c00a85af6476f67f
(cherry picked from commit 13c923d00a8a605db7aecac7456ecfdd08d18759)
Change-Id: Iec8cdd30ad5e4979d56140a8c00a85af6476f67f
3 files changed