json: add -wide mode with word-level net indices

[widlarizer]

For well-behaved designs, Yosys passes bufnorm -nomode -buf -chain; splice -wires can be safely used to normalize the design such that we eliminate SigSigs and slicing and concatenation in SigSpecs. By default, the json backend implements slicing/concatenating SigSpecs by representing all values as concatenations of bits. If a yosys json consumer tool is free to do the aforementioned normalization, this PR allows it to use word-level net indices instead

Example cell: notice "connections"

        "$not$tests/sat/alu.v:50$10": {
          "hide_name": 1,
          "type": "$not",
          "parameters": {
            "A_SIGNED": "00000000000000000000000000000000",
            "A_WIDTH": "00000000000000000000000000001000",
            "Y_WIDTH": "00000000000000000000000000001000"
          },
          "attributes": {
            "src": "tests/sat/alu.v:50.18-50.20"
          },
          "port_directions": {
            "A": "input",
            "Y": "output"
          },
          "connections": {
            "A": 1250077441,
            "Y": -132126554
          }
        }

• add test
• help string
• enumerate nets instead of dumping hashidx_
• normalization probably depends on opt_clean: handle undriven and x-bit driven bits consistently #5004 being available to work consistently