Reland "libutils: Introduce StaticString16""

This reverts commit 1270e4fbf17402fb01dbfa7928a654d41d8553ee.

Bug: 138856262
Test: Run unit tests.
Change-Id: I37be01d7d4f98a83078870cb0917275336fa2bbd
Merged-In: I8da93f2c9b95183e32d4a2ea895f90c449abbe4d
6 files changed