[slang][port] Fix bugs

[Kitaev2003]

Hello!

1. This code is not serializing to json correctly. So I fixed PortConnection::serializeTo.

module top;
    wire[1:0] net1;
    m loc({net1});
endmodule

module m({net1, net2});
    input wire net1, net2;
endmodule

serialization before:

"connections": [
  {
    "port": "2199025177616 ",
    "expr": {
      "kind": "Concatenation",
      "type": "logic[1:0]",
      "operands": [
        {
          "kind": "NamedValue",
          "type": "logic[1:0]",
          "symbol": "2199025173856 net1"
        }
      ]

serialization now

"connections": [
  {
    "port": {
      "name": "",
      "kind": "MultiPort",
      "addr": 2199025177616,
      "type": "logic[1:0]",
      "direction": "In",
      "ports": [
        {
          "type": "logic",
          "direction": "In",
          "internalSymbol": "2199025175320 net1"
        },
        {
          "type": "logic",
          "direction": "In",
          "internalSymbol": "2199025175720 net2"
        }
      ]

2. When running a debug build on this code:

module top;
    wire net1;
    m loc({net1});
endmodule

module m({net1, net2});
    input wire net1, net2;
endmodule

 internal compiler error: Assertion 'in == internal.end() && ex == external.end()' failed
  in file /etc/slang/source/ast/symbols/PortSymbols.cpp, line 1982
  function: void slang::ast::PortConnection::checkSimulatedNetTypes() const

Slang was crashing with an assert. I couldn't understand why this assert was needed. I think it should just be removed from the code.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.71%. Comparing base (4afa7a2) to head (dacb174).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1043      +/-   ##
==========================================
- Coverage   94.71%   94.71%   -0.01%     
==========================================
  Files         191      191              
  Lines       47658    47656       -2     
==========================================
- Hits        45138    45136       -2     
  Misses       2520     2520              

Files	Coverage Δ
source/ast/symbols/PortSymbols.cpp	97.83% <100.00%> (-0.01%)	⬇️

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