Clean up netci.groovy (#15030)

Clean up netci.groovy (#15030)

* Clean up netci.groovy

1. Don't repeat entire list of JIT stress and R2R scenarios over and over;
use functions to check for scenario groups.
2. Merge handling of R2R baseline and stress scenarios.
3. Add function to determine if a scenario is a JIT stress scenario.
4. Fix JIT stress mode display name generator to handle CoreFx tests
as well, preserving the way they are currently displayed.
5. Fix R2R display name generator to handle baseline R2R scenario.
6. Fix bug where x86 R2R baseline job wasn't created.
7. Fix bugs where triggering some jobs, such as R2R jobs, would trigger lots
of other jobs with insufficient trigger strings. Thus, more trigger strings
now have architecture + scenario in them. E.g., "Innerloop" jobs now much
be triggered using a phrase containing "Innerloop".
8. Simplify code that creates builds, and test run commands.
9. Fix mis-casing of COMPlus_JITMinOpts in R2R stress list.
10. Expand list of valid ARM Windows scenarios to match total list of
scenarios, but with some scenarios commented out. Add the
jitstress2 + jitstressregs to the acceptable list. Add note about the
many scenarios in this list that are not in the full scenario list. Add
function to determine if a scenario is in this list.
11. Support crossgen of frameworks using altjit
12. Don't support 'r2r' scenario on arm/armlb/arm64 Windows.