i#6938 sched migrate: Add scheduler statistics

[derekbruening]

Adds schedule statistics to memtrace_stream.h. Implements these statistics in the streams returned by scheduler_t. This initial round includes the following values:

[scheduler] Stats for output #0
[scheduler]   Switch input->input      :        16
[scheduler]   Switch input->idle       :         4
[scheduler]   Switch idle->input       :         3
[scheduler]   Switch nop               :       119
[scheduler]   Quantum preempts         :       131
[scheduler]   Direct switch attempts   :         0
[scheduler]   Direct switch successes  :         0

The switches are split into those 4 categories to make it easier to compare to other sources of switch counts, such as perf where perf limited to a cgroup or process will be missing the idle->input switches, or schedule_stats which is missing the input->idle today.

Adds checks that these match the schedule_stats tool's values.

Adds tests of the values to several key scheduler unit tests.

Issue: #6938

[derekbruening]

a64-sve failure is the very flaky #3320

[brettcoon]

A couple suggestions.

[derekbruening]

I also split the switches into 4 categories. Maybe there are enough changes to warrant another review.

Here is an example output now:

$ bin64/drrun -t drmemtrace -indir drmemtrace.threadsig.5* -tool schedule_stats -core_sharded -cores 3 -verbose 1 -sched_quantum 50000
Core #0 schedule: AaaaCBCBCccDEeeDCDCEBDCE_B_C_C_
Core #1 schedule: BE_CDCDECBECBDEDBCDBEBDddBbbbbDECBbA_E__
Core #2 schedule: CD_DBEDEDBDCDECBEBECEeeBEDECDCDCDCDCDCDCDCDCDCEDCDCDCDCDCBECEDd_C_D_D_C_C_C
[scheduler] Stats for output #0
[scheduler]   Switch input->input      :        16
[scheduler]   Switch input->idle       :         4
[scheduler]   Switch idle->input       :         3
[scheduler]   Switch nop               :       119
[scheduler]   Quantum preempts         :       131
[scheduler]   Direct switch attempts   :         0
[scheduler]   Direct switch successes  :         0
[scheduler] Stats for output #1
[scheduler]   Switch input->input      :        26
[scheduler]   Switch input->idle       :         3
[scheduler]   Switch idle->input       :         2
[scheduler]   Switch nop               :       106
[scheduler]   Quantum preempts         :       129
[scheduler]   Direct switch attempts   :         0
[scheduler]   Direct switch successes  :         0
[scheduler] Stats for output #2
[scheduler]   Switch input->input      :        57
[scheduler]   Switch input->idle       :         7
[scheduler]   Switch idle->input       :         7
[scheduler]   Switch nop               :        86
[scheduler]   Quantum preempts         :       135
[scheduler]   Direct switch attempts   :         0
[scheduler]   Direct switch successes  :         0