Enhance AUTO_TEMPLATE for unpacked array connections and merging

[anythingelse0]

Summary

Add support for connecting one element of an unpacked array per instance
in an AUTO_TEMPLATE, and have AUTOWIRE/AUTOINPUT declare the net as an
unpacked array covering all connected indexes.

module InstModule
  (
   output [3:0] ptl_mapvalidx
   );
endmodule

module top ();
   /*AUTOWIRE*/
   /*
    InstModule AUTO_TEMPLATE
    (
    .ptl_mapvalidx (ptl_mapvalid[].[@]),
    );
    */
   InstModule ms2m
     (/*AUTOINST*/);
   InstModule ms0m
     (/*AUTOINST*/);
endmodule

expands it to:

module top ();
   /*AUTOWIRE*/
   // Beginning of automatic wires (for undeclared instantiated-module outputs)
   wire [3:0] ptl_mapvalid [0:2];   // From ms2m of InstModule.v, ...
   // End of automatics
   /*
    InstModule AUTO_TEMPLATE
    (
    .ptl_mapvalidx (ptl_mapvalid[].[@]),
    );
    */
   InstModule ms2m
     (/*AUTOINST*/
      // Outputs
      .ptl_mapvalidx                (ptl_mapvalid[2]/*[3:0].[2]*/)); // Templated
   InstModule ms0m
     (/*AUTOINST*/
      // Outputs
      .ptl_mapvalidx                (ptl_mapvalid[0]/*[3:0].[0]*/)); // Templated
endmodule

Implementation

• verilog-auto-inst-port: rewrite sig[].[idx] so only the unpacked
  index stays executable; the port ranges go into a /*[bits].[idx]*/
  comment (extending the existing comment convention used for memory
  ports), keeping the connection legal Verilog.
• verilog-read-sub-decls-expr: canonicalize the comment back into an
  unpacked range so AUTOWIRE and friends can parse it; numeric indexes
  become single-element ranges ([2:2]), non-numeric indexes pass
  through unchanged.
• verilog-signals-combine-bus: merge ascending numeric unpacked ranges
  via min/max into one covering range, the same way packed bits are
  merged. Overlapping or duplicate ranges merge silently — an
  unpacked-array net fanned out to several instances must not warn.
  ", Couldn't Merge" is kept only when a numeric range mixes with an
  unmergeable form (descending like [3:0], or symbolic like [IDX]),
  in which case the first unmergeable form wins so existing declarations
  keep their direction/expression.
• [].[@] on an instance whose name provides no value for @ now
  raises an error instead of silently emitting a nonsense connection.

Tests

• tests/autoinst_tpl_array_index.v: basic expansion, duplicate element
  index (merges to a single-element range), non-numeric index.
• tests/tpl_arr_edge.v: non-consecutive indexes, descending packed +
  ascending unpacked, multiple ports per template, mixed
  mergeable/unmergeable forms, hard-coded index gaps, single instance,
  descending instance order, overlapping ranges, signed ranges,
  descending-vs-numeric and symbolic-vs-numeric conflicts, negative
  single index, escaped identifiers, and a fanout regression test
  (unpacked-array input feeding two instances stays warning-free in
  AUTOINPUT).

[anythingelse0]

• Remove inapplicable documentation about unpacked arrays in AUTOWIRE
• Apply formatting suggestion to unpacked array documentation
• Improve comment clarity for unpacked declaration handling"

[wsnyder]

Looks good, I pushed some minor indent cleanups. As these changes are non-trival you need to email assign@fsf.org and complete a copyright assignment. Let me know when done and the name to commit under; Emacs does not allow anonymous commits.