Add multi-workload support to record_filter

Attempting to create a multi-workload core-sharded-on-disk trace fails today:
```
$ rm -rf foo; mkdir foo; bin64/drrun -t drmemtrace -tool record_filter -core_sharded -cores 4 -sched_block_scale 0.001 -multi_indir ../src/clients/drcachesim/tests/drmemtrace.threadsig.x64.tracedir:../src/clients/drcachesim/tests/drmemtrace.threadsig.x64.tracedir -outdir foo
```

Fails with record_filter saying "Multi-workload inputs not yet supported". It needs to augment all its PC keys to include the workload ordinal.

This issue also covers regenerating the checked-in threadsig-core-sharded trace and adding tests of properly getting unique tid values from #7401.