[VMR][mono] Check in AOT offsets file(s), remove offsets jobs from official build

[steveisok]

In the runtime official build, the first step in building mono cross compilers requires generating offset files in a separate job and is later consumed in another job that produces the binaries. This approach makes a VMR vertical build more difficult because we cannot express "build all artifacts for linux-arm64" in one go without depending on a separate job.

• Produce offset files locally and check them into the runtime repo
• Adjust build to pick them up from the source tree instead of where azdo places them now
• Add some kind of validation job to make sure the offset files are up to date

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[mmitche]

@akoeplinger What's the status of this?