better support for struct array parameters

This includes support for
- parsing dimensioned alias parameters
- flattening non-var decls with multiple packed dimensions
- converting arrays of structs
- inferring struct types for decls with initializations

test/basic/struct_array_param.sv

@@ -0,0 +1,17 @@
+typedef struct packed {
+    logic [2:0] a;
+    logic [1:0] b;
+    logic [3:0] c;
+} foo_s;
+
+parameter foo_s [1:0] foo = {
+    '{ a: 2, b: 1, c: 0 },
+    '{ a: 1, b: 0, c: 2 }
+};
+
+module top;
+    initial begin
+        $display(foo[0]);
+        $display(foo[1]);
+    end
+endmodule