Improve dictionary printing to avoid confusion with arrays

- Add leading and trailing spaces within dictionaries, as the `{}`
  characters are hard to distinguish from `[]` on some fonts.
  This is especially helpful with empty arrays and dictionaries.

modules/gdscript/tests/scripts/parser/features/dictionary.out

@@ -7,8 +7,8 @@ null
 false
 empty array
 zero Vector2i
-{22:{4:["nesting", "arrays"]}}
-{4:["nesting", "arrays"]}
+{ 22: { 4: ["nesting", "arrays"] } }
+{ 4: ["nesting", "arrays"] }
 ["nesting", "arrays"]
 nesting
 arrays

modules/gdscript/tests/scripts/parser/features/dictionary_lua_style.out

@@ -1,2 +1,2 @@
 GDTEST_OK
-{"a":1, "b":2, "with spaces":3, "2":4}
+{ "a": 1, "b": 2, "with spaces": 3, "2": 4 }

modules/gdscript/tests/scripts/parser/features/dictionary_mixed_syntax.out

@@ -1,2 +1,2 @@
 GDTEST_OK
-{"hello":{"world":{"is":"beautiful"}}}
+{ "hello": { "world": { "is": "beautiful" } } }

modules/gdscript/tests/scripts/parser/features/nested_dictionary.out

@@ -1,5 +1,5 @@
 GDTEST_OK
-{8:{"key":"value"}}
-{"key":"value"}
+{ 8: { "key": "value" } }
+{ "key": "value" }
 value
 value