Fix missing encoding of nested maps in typescript bindings (#11746)

The encoder just took the keys & values as is which clearly falls
apart once those actually contain anything else that requires encoding

changelog_begin

- [Typescript Bindings] Fix an issue where nested maps did not get
  encoded properly before sent to the JSON API which caused requests
  to fail with a decoding error on the JSON API.

changelog_end

language-support/ts/daml-types/index.test.ts

@@ -71,6 +71,15 @@ describe('@daml/types', () => {
       expect(m2.get(k)).toEqual(makeArr(m2.values())[makeArr(m2.keys()).findIndex((l) => _.isEqual(k, l))]);
     }
   });
+  it('nested genmap', () => {
+    const {encode, decoder} = Map(Text, Map(Text, Text));
+    const decoded: Map<Text, Map<Text, Text>> =
+      emptyMap<Text, Map<Text, Text>>().set("a", emptyMap<Text, Text>().set("b", "c"));
+    const decode = (u: unknown): Map<Text, Map<Text, Text>> => decoder.runWithException(u);
+    const encoded = [["a", [["b", "c"]]]];
+    expect(encode(decoded)).toEqual(encoded);
+    expect(decode(encoded)).toEqual(decoded);
+  });
 });
 
 test('memo', () => {

language-support/ts/daml-types/index.ts

@@ -518,5 +518,5 @@ export const emptyMap = <K, V>(): Map<K, V> => new MapImpl<K, V>([]);
  */
 export const Map = <K, V>(kd: Serializable<K>, vd: Serializable<V>): Serializable<Map<K, V>> => ({
   decoder: jtv.array(jtv.tuple([kd.decoder, vd.decoder])).map(kvs => new MapImpl(kvs)),
-  encode: (m: Map<K, V>): unknown => m.entriesArray(),
+  encode: (m: Map<K, V>): unknown => m.entriesArray().map(e => [kd.encode(e[0]), vd.encode(e[1])]),
 });