Revert naming test-proxy

[scbedd]

This PR updates the matrix to also pass through the assembly name, as we can't automagically infer which of the files in the standalone matrix is a .exe on linux/mac.

Save ourselves the downstream pain of:

• not aligning with the namespace (which plays hell with the .net usage of this thing)
• needing to worry about name squatters (generic test-proxy being the name :|)
• fixing the numerous other places I have probably broken stuff by the rename

Just...just save myself the pain.

spoiler alert

I did not save myself anything unfortunately. I have discovered all of these issues with the latest eng/common update that involves this. Reverting, updating that eng/common one last time, and hopefully being done with this.

[scbedd]

Real talk though I think this was an ill-advised change to make the standalone executable a bit nicer to use. At the end of the day I don't think that anyone will really care about the difference between test-proxy and azure.sdk.tools.testproxy when it's the same binary under the hood.

[scbedd]

This is going to require another update of azure-sdk-build-tools to fix, due to the fact that the method of detecting the binary is flawed.

It's my code so I can't be sad about it.

[scbedd]

This is going to come through the same avenue as a previous build that required azure-sdk-build-tools update. Will kludge these changes into the automatically submitted sdk-build-tools reference update. Closing.

[scbedd]

This PR is now reflected in the sdk-build-tools update PR.