Enable compiling with `crossgen2` (#32508)

* Enable compiling Asp.NET with crossgen2

* Use use linux crossgen2 instead of linux-musl crossgen2 when targetting linux-musl from the build

* Attempt to make musl work

* Fix typo

* Use correct bits to compile take #3

* Add Pgo data

* Fix mistaken at symbol

* Move to Core-Eng build agents
- should resolve problems w/ disk space in "Tests: Helix ARM64 matrix" job
- need `node` in this job for some reason

* Remove `crossgen` tool infrastructure
- remove many properties related only to the `crossgen` tool
  - may have missed a few of course

nits:
- `crossgen` -> `crossgen2` in a few comments
- add / expand a few comments to improve clarity

Co-authored-by: David Wrighton <davidwr@microsoft.com>