Running and visualizing tests in AzureDevOps (Part 1) (dotnet/coreclr#21502)

Running and visualizing tests in AzureDevOps (Part 1) (dotnet/coreclr#21502)

* Enable Azure Pipelines reporter so the test results can be seen at one place (i.e. "Tests" tab) - TestRunNamePrefix should encode all the needed information for a test run to be identifiable.

* Scenarios property should use comma (not semi-colon) to work correctly on non-Windows.

* Specify timeout to test jobs (the numbers are taken from netci.groovy) - we would adjust them as soon as we get this running in each PR.

* Specify timeout for Helix work items (the number is taken from buildpipeline) - same as above.

* Specify helixType and helixRepo properties to the job and use _HelixType and _HelixSource variables in MSBuild project instead of defining them manually.

*  Limit Pri0 Checked test jobs to running against pull requests. This also should be limited in the future to "default" build definition name - so when we have PR workload selection feature working we can distinguish between default PR validation and user triggered jobs.

* Remove "Prepare tests for helix" step - instead of archiving Core_Root and tests folders ourselves - directly specify them as correlation payload and work item payload directories and let the archiving be handled by Helix Sdk.

Commit migrated from https://github.com/dotnet/coreclr/commit/ef7afc8e86eb1d8407a1c07ae735158efc5aca75