Trace processor tests: big move pt. 1

Create four main subdirectories in diff_tests/:
- stdlib
- metrics
- syntax
- parser

and move most of the tests into these four directories.
The remaining non-moved directories (to be moved in a follow-up):
- android
- chrome
- graphics
- power
- tables

Non-mechanical changes:
- split network metrics and parsing
- split memory metrics and parsing
- split performance into parser/sched and metrics/frame_timeline
- move profiling/metrics_tests.py into metrics/profiling and the rest into parser/profiling
- fold scheduler into parser/sched
- move translation into parser/translated_args

Change-Id: I46b7f6ea4d3bba3e8dc2e4402d437dc35ebc3393