i#6635 core filter, part 5: schedule_stats

[derekbruening]

Changes schedule_stats to detect switches via <workload,tid> instead of the input ordinal, to support core-sharded-on-disk traces.

Updates schedule_stats_test which no longer needs its own mock stream if we add get_input_interface to default_memtrace_stream_t and call set_tid.

Adds a schedule_stats end-to-end test on the checked-in core-sharded-on-disk trace to ensure switches are detected.

Issue: #6635

[abhinav92003]

This branch needs to be updated post #6700 but I guess it doesn't hinder review that much so I'll continue.

[derekbruening]

Xref #6685