[ImportVerilog][CAPI] Add interfaces to allow external use

[SpriteOvO]

This PR adds C-API for ImportVerilog stuff to allow external use.

[uenoku]

I wonder there is better direction. I understand we did the same thing for firtool but the maintainability has not been good. Instead I'm curios we can use some string serialization (similar to what we are doing for ExportVerilog lowering option) or MLIR attribute as a way to pass option .

[SpriteOvO]

@uenoku I do agree that the maintainability of such options structs is poor.

@sequencer If we change the options structs to something like a CLI arguments string, would that be acceptable to you guys?

[sequencer]

If we change the options structs to something like a CLI arguments string, would that be acceptable to you guys?

I think we only need to expose these options to C-API to allow external program to use import Verilog as library.

For C-API about MlirImportVerilogOptions, it can be safe and looks more like what https://github.com/llvm/circt/blob/firtool-1.122.0/include/circt-c/Firtool/Firtool.h does.