Add serialization to libkll

Serialization support has been added to google3. In this CL, we are
updating the libkll code to match these google3 updates.

Bug: 184550826
Bug: 182225759
Test: atest libkll_test libkll-encoder_test
Change-Id: I6f4877886c9b4d66fe7afb021a564aa1097545f5
23 files changed