Make TableLogBufferFactory thread-safe.

It's possible for 2 threads to call TableLogBufferFactory#getOrCreate at
the same time with the same name, and we don't want the factory to
incorrectly create two separate instances of TableLogBuffer with the
same name. (If it did, then DumpManager#registerTableLogBuffer would
throw an IllegalArgumentException.)

Fixes: 391803434
Flag: EXEMPT bugfix
Test: SysUI compiles
Test: atest TableLogBufferFactoryTest
Change-Id: Icce197acab9b6858bea98779cd46b80947de6cac