Cache process info where possible and dispose Process objects.

[Erarndt]

Fixes #

Context

There are multiple places where information about the current process is retrieved. There is a non-trivial cost to getting this information and the Process objects should be disposed to avoid additional GC cost due to the finalizer running. This change adds properties in EnvironmentUtilities that cache info such as the current process ID (this implementation is copied from .NET 6), and in some instances, updates some callers to dispose of the Process object for uncommon usages.

Changes Made

Testing

Notes

[JanKrivanek]

Related to #11160

[SimaTian]

I tried rebasing and/or merging with main, which made a mess.
In the end, I opted for checking out main, cherrypicking the commit & then fixing one issue with some old files being re-added by it.
Review will follow.
cc: @Erarndt

[SimaTian]

I've left some comments. Overall I like it.
Ping me when ready please and I'll approve.

[JanKrivanek]

Thank you!
Overall looks ready to go!

[rainersigwald]

I was experimenting with adding these to our banned-API list and found a few uses which would benefit from a long-lived Process.GetCurrentProcess() to call other methods/properties on it. Would that cause a problem or should we consider it?

[SimaTian]

LGTM

[SimaTian]

I talked with @AR-May and this has an impact that is below what we can detect with PerfStar. At least it is definitely not a regression and since it is a neat code cleanup, I'm voting for merge.