Initial scaffolding and partial implementation of ilasm in C#

[jkoritzinsky]

Start an implementation of ilasm in C# in src/tools/ilasm. ANTLR4 is used to build the grammar.

I decided to structure it as a library (with a frontend to come later) to match ILVerify/ILVerification.

This implementation is far from complete. The grammar is missing any updates from the last year or two and much is untested and unimplemented.

It has one passing test for a simple case so far.

Putting out a PR now so other team members and community members can work on it.

Contributes to #121847

[huoyaoyuan]

This is a great advantage of keeping ilasm/ildasm in C++

I think we can continue the discussion in #121847. Since the metadata reader is expected to be replaced by DNMD, the precondition can change here.

[jkotas]

How are we expected to collaborate on this? Apparently it needs to fulfill more functionalities. Should we merge it as scaffold and open more PRs?

Yes, it is the idea.

I would like to confirm that we don't care about losing such an ability.

I do not mind with losing this. We actually reached a point where it tends to be easier to prototype new functionality like that in NAOT first. NAOT uses managed System.Reflection.Metadata.

Since the metadata reader is expected to be replaced by DNMD

This is not a committed plan. (If we were to do this, it needs to come with measurable user-observable improvements and it needs to replace the existing metadata reader completely.)

[jkoritzinsky]

Marking this as ready-for-review as I've done some cleanup and I think this is in a decent state to be experimental in main.

[jkotas]

It is hard to review a code bomb like this in details. I have only done a cursory review. LGTM

[MichalStrehovsky]

[jkoritzinsky]

I apologize for the code bomb. My initial intention of finishing this project as a holiday hackathon a few years back and breaking out the work into multiple (more manageable) PRs didn't exactly work out.

[jkoritzinsky]

/ba-g unrelated timeout in threading tests.