Remove run.exe and config.json (#21608)

Remove run.exe and config.json (#21608)

This moves us one step away from buildtools and towards arcade.

This replaces run.sh and run.cmd (and all invocations) with "dotnet.sh msbuild" and "msbuild.cmd".
- I'm using these wrapper scripts for now instead of those in eng/common in order to retain the very helpful "Running <command>" output in the build logs.
- I'm using msbuild.cmd instead of dotnet.sh to match the current behavior that uses desktop msbuild on windows, instead of dotnet.

All of the arguments that used to be implicitly generated by run.exe and config.json are now explicit, resulting in longer (but easier to copy+paste) commands. Some of these arguments are likely unnecessary, but in this change my goal is just to match the run.exe behavior. Later, I would like to go through and clean up parameters that don't need to be passed in every invocation. I might also consider moving more of the common arguments out into variables in a later change.

Some of the wrapper scripts now have limited support for parsing "-Argument=Value" style parameters, to support our existing buildpipeline infrastructure, since I thought this was easier to test than changing our buildpipeline definitions. We can remove that parsing logic once we stop using buildpipeline (which has happened at this point).

Some subtle parts of the change:

* Add msbuild.cmd

This simulates the behavior of Tools\msbuild.cmd, which calls desktop msbuild.

* Fix BuildOS processing in package build and publish

Previously, config.json had its own processing that would set
OSName. Instead, we now pass it in explicitly where it's
needed (building packages), or not at all (publishing them).

* Handle "=" in publish-packages.cmd and other scripts

This seems necessary to properly handle the azure access token

* Set __BuildOS in PublishPackages

Required for cases where the build OS isn't detected during the build
such as freebsd.

* Use dotnet msbuild in runtest.py

This prevents us from having to deal with different quote escape
behavior on windows and linux. Previously, arguments like
fileloggerparameters and the logger were given quotes to escape
semicolons in the argument. On unix, this prevented the argument from
being split up by bash. On windows, it seems that the run.cmd/run.exe
tools would prevent the extra quotes from being passed to
msbuild.exe (desktop msbuild would choke on the quotes if they were
passed along).

Unlike desktop msbuild, dotnet msbuild is able to parse the quoted
strings, so we simply psas the quoted arguments directly to it on
windows. We may be able to do the same on unix.

* Fix build-test.sh problem with BuildOS

When copying native files during the unix test build, we rely on
__BuildOS being set. Fixing the import order and always setting
__BuildOS fixes this. We should eventually fix the inconsistent use of
BuildOS vs __BuildOS.