[ExtensionsMetadataGenerator] Remove assembly loading requirement

[brettsam]

We should move the EMG to use something like Mono.Cecil, which would allow us to inspect assemblies without needing to load all of their dependencies. Would eliminate issues like we've found with #4055.

[mhoeger]

@brettsam - what's the priority on this? Should we move it to triaged or do you want it assigned to an upcoming sprint?

[brettsam]

It's not super-urgent. I'll move this to Triaged. I actually have a prototype already but it'd need some testing/validation still. We can do it in a future sprint.