[ImportVerilog]: Create variables for function arguments

[Max-astro]

Adds shadow variables for SV function arguments.
Fixes: #7431

Adjusts two test cases test/Conversion/ImportVerilog/basic.sv and test/Conversion/ImportVerilog/builtins.sv

Adds two test functions in test/Conversion/ImportVerilog/builtins.sv, which will crash in the former circt-verilog tool.

[hailongSun2000]

LGTM! Thank @Max-astro for your work on this error(#7431).

[hailongSun2000]

@fabianschuiki: And if the user never assigns to the variable, the canonicalizers will get rid of it automatically again later 😃

If you want IR to stay the same when using --canonicalize like

func.func private @dummyE(%arg0: !moore.i1) -> !moore.i1 {
    return %arg0 : !moore.i1
}

You have to implement the VariableOp::Canonicalize() manually. But you can add this in the new PR 😄.

[fabianschuiki]

Awesome, thanks for implementing this!

If you want to get rid of all the changes in the SV tests, you could do what @hailongSun2000 has suggested and try to delete the variables again if they were not needed. That should make most tests see no real change at all, which may be beneficial? Let me know what you think 😃 I'm also very happy with just landing this!

[fabianschuiki]

Very cool, thanks a lot for doing all this work!

[Max-astro]

Very cool, thanks a lot for doing all this work!

I really appreciate the guidance you provided, it means a lot to me that you took the time to help.

[hailongSun2000]

So cool!

[hailongSun2000]

Can I merge it? @Max-astro

[Max-astro]

Can I merge it? @Max-astro

Sure, I'm glad to hear that.

[fabianschuiki]

Fantastic, thanks for merging @hailongSun2000 and thanks for fixing this bug @Max-astro 🥳!