Add no tiered compilation test jobs (dotnet/coreclr#18864)

Add no tiered compilation test jobs (dotnet/coreclr#18864)

* Add no tiered compilation test jobs

With the upcoming switch to make tiered compilation on by default we want to preserve some JIT testing that will not enable tiered compilation.
1) Add 'no_tiered_compilation_pri0' jit stress job, logically the non-tiered variant of current 'Innerloop' jobs
   - This job will run on all PRs for Checked x (Windows x86, Windows x64, Ubuntu arm) - but not scheduled that way for the moment so it can be tested post-checkin
2) Add 'no_tiered_compilation' jit stress job, logically the non-tiered variant of the current 'normal' job
   - This job has the same periodic schedule as other jit stress jobs
3) Add 'r2r_no_tiered_compilation' r2r stress job, logically the non-tiered variant of the current 'r2r' job
   - This job has the same periodic schedule as other r2r stress jobs

Misc adjustments - Added isPri0TestScenario because 'innerloop' is no longer the only scenario name which has this property + eliminated various comments that implied 'innerloop' IFF pri0

Commit migrated from https://github.com/dotnet/coreclr/commit/37322ac660acffa1543d8338c118417d48571f1c