Update PMI asm diffs in the CI (#20743)

Update PMI asm diffs in the CI (#20743)

* Respond to PMI asm diffs code review feedback

Add some try/finally code to improve robustness.
Remove direct invocation of run.cmd.

Also, simplify the generated asm directory hierarchy.

* Improve PMI script error code

Only return non-zero if there is a fatal error. For non-fatal error,
such as the existence of asm diffs, return zero. This will allow
subsequent "build" steps in netci.groovy to run, namely, the
archiving of the asm directory.

Later, determine a better way figure out how to deal with the existence
of asm diffs.

* Update dotnet SDK download links