[Feature] Tentative struct definition for type parameter declaration

[taichi-ishitani]

I'm rewriting a SV module having type parameter assumed to be overwritten by struct type.
I put logic to this kind of parameter as tentative type.
https://github.com/pezy-computing/pzbcm/blob/8f796eb5e83ce8fbadbbc93aea1012f680fadd3f/pzbcm_min_max_finder/pzbcm_min_max_finder.sv#L11

During building Veryl version of this module I got following errors because default value of RESULT is logic and logic does not have data and location members.

[INFO ]   Processing file (/home/ishitani/workspace/pzbcm_veryl/pzbcm_min_max_finder/pzbcm_min_max_finder.veryl)
Error:   × veryl check failed

Error: unknown_member (https://doc.veryl-lang.org/book/06_appendix/02_semantic_error.html#unknown_member)

  × "result" doesn't have member "data"
    ╭─[/home/ishitani/workspace/pzbcm_veryl/pzbcm_min_max_finder/pzbcm_min_max_finder.veryl:63:1]
 63 │     if next_n == 1 {
 64 │       result.data     = next_data[0];
    ·       ───┬──
    ·          ╰── Error location
 65 │       result.location = next_location;
    ╰────
  help:
Error: unknown_member (https://doc.veryl-lang.org/book/06_appendix/02_semantic_error.html#unknown_member)

  × "result" doesn't have member "location"
    ╭─[/home/ishitani/workspace/pzbcm_veryl/pzbcm_min_max_finder/pzbcm_min_max_finder.veryl:64:1]
 64 │       result.data     = next_data[0];
 65 │       result.location = next_location;
    ·       ───┬──
    ·          ╰── Error location
 66 │     } else {
    ╰────
  help:

To resolve this kind of problem, I'd like Veryl to have a notation to describe required members for a param type declaration like below.

param RESULT: type = struct(data, location)