TracedOrdinal per-frame optimizations

Optimizes TracedOrdinal by only doing work inside the trace method when
tracing is enabled, and by deferring the generation of the *Negative
variant (which involves a StringPrintf) until the first time the
variable is traced.

Test: atest libsurfaceflinger_unittest
Bug: 153112939
Change-Id: I14e316797c032b78fb2ed99c3a7db5b59a470845