several major fixes surrounding packed arrays

- entirely new PackedArray conversion (always flattens)
- typedef and struct correctly order packed ranges when combining types
- Stmt LHS traversal no longer traverses nested statements to avoid double conversion
- Logic conversion applies to `initial` blocks`
- new and modified tests to cover these cases

test/basic/struct_array.sv

@@ -0,0 +1,17 @@
+typedef struct packed {
+    logic x;
+    logic [3:0] y;
+    logic [1:0] z;
+} Struct_t;
+
+module Unpacker(in, select, a, b, c);
+    parameter WIDTH = 8;
+    input Struct_t [WIDTH-1:0] in;
+    input logic [$clog2(WIDTH)-1:0] select;
+    output logic a;
+    output logic [3:0] b;
+    output logic [1:0] c;
+    assign a = in[select].x;
+    assign b = in[select].y;
+    assign c = in[select].z;
+endmodule