Reland "libutils: Introduce StaticString16""

This time with old branches excluded.

Bug: 138856262
Test: Run unit tests.
Change-Id: Id0bb1d54b71e38244d64f1b684db1fda81de854c
Merged-In: I8da93f2c9b95183e32d4a2ea895f90c449abbe4d
6 files changed