feat(compiler): allow map to be valid json (#4186)

Fixes #3894

Not sure if it was explicitly left out for a reason. For literals, it obviously looks a little ugly, but there's no logical issue as far as I can see.

*By submitting this pull request, I confirm that my contribution is made under the terms of the [Wing Cloud Contribution License](https://github.com/winglang/wing/blob/main/CONTRIBUTION_LICENSE.md)*.

examples/tests/valid/json.main.w

@@ -3,7 +3,13 @@ bring cloud;
 let jsonNumber  = Json 123;
 let jsonBool    = Json true;
 let jsonArray   = Json [ 1, 2, 3 ];
+let jsonMap     = Json { "1" => 1, "2" => 2, "3" => 3 };
 let jsonObj     = Json { boom: 123 };
+
+for j in [jsonNumber, jsonBool, jsonArray, jsonMap, jsonObj] {
+  assert(j == Json.parse(Json.stringify(j)));
+}
+
 let jsonMutObj = MutJson {
   hello: 123,
   world: [ 1, "cat", 3 ],

libs/wingc/src/type_check.rs

@@ -1148,6 +1148,7 @@ impl TypeRef {
 			Type::MutJson | Type::Json(None) => true,
 			Type::Inferred(..) => true,
 			Type::Array(v) => v.is_json_legal_value(),
+			Type::Map(v) => v.is_json_legal_value(),
 			Type::Optional(v) => v.is_json_legal_value(),
 			Type::Struct(ref s) => {
 				for (_, t) in s.fields(true) {

tools/hangar/__snapshots__/test_corpus/valid/json.main.w_compile_tf-aws.md

@@ -98,7 +98,11 @@ class $Root extends $stdlib.std.Resource {
     const jsonNumber = 123;
     const jsonBool = true;
     const jsonArray = [1, 2, 3];
+    const jsonMap = ({"1": 1,"2": 2,"3": 3});
     const jsonObj = ({"boom": 123});
+    for (const j of [jsonNumber, jsonBool, jsonArray, jsonMap, jsonObj]) {
+      {((cond) => {if (!cond) throw new Error("assertion failed: j == Json.parse(Json.stringify(j))")})((((a,b) => { try { return require('assert').deepStrictEqual(a,b) === undefined; } catch { return false; } })(j,(JSON.parse(((args) => { return JSON.stringify(args[0], null, args[1]?.indent) })([j]))))))};
+    }
     const jsonMutObj = ({"hello": 123,"world": [1, "cat", 3],"boom boom": ({"hello": 1233})});
     const message = "Coolness";
     ((obj, args) => { obj[args[0]] = args[1]; })(jsonMutObj, ["hello",message]);