[ImportVerilog] Add support for specialized parametric classes

[Scheremo]

• Add support for lowering specialized (instantiated) generic classes by embedding actual parameter values into the fully-qualified class symbol, e.g. @"pkg::MyClass#(.P(1),.Q(8))".
• Explicitly skip GenericClassDefSymbol (unspecialized templates) per IEEE 1800-2023 §8.25; only specialized ClassType symbols are lowered.
• Ensure class bodies are emitted once.
• Make type lowering declare/convert the class declaration eagerly to keep symbol references consistent.

[TaoBi22]

LGTM modulo nits, super cool how clean a diff this is!

[fabianschuiki]

LGTM! I'm wondering if we should even include the parameters in the class name at all. Modules had a similar monomorphization going on, and we decided to not have the parameters in the name to keep things at least somewhat readable when parameters get out of hand. It's okay to pick the same class name multiple times -- symbolTable.insert(...) will uniquify the classes to ensure they are distinct. We could always add a dbg.variable "WIDTH", %constWidth op to the class body to capture the values of the parameters.

[Scheremo]

LGTM! I'm wondering if we should even include the parameters in the class name at all. Modules had a similar monomorphization going on, and we decided to not have the parameters in the name to keep things at least somewhat readable when parameters get out of hand. It's okay to pick the same class name multiple times -- symbolTable.insert(...) will uniquify the classes to ensure they are distinct. We could always add a dbg.variable "WIDTH", %constWidth op to the class body to capture the values of the parameters.

Fair enough. If we change our minds it'll be very easy to add it back.