sync: add Map.CompareAndSwap and Map.CompareAndDelete

These methods were added in Go 1.20 but were missing from TinyGo's
sync.Map implementation, causing compilation failures for code that
uses them.

The implementation follows the same lock-based approach as the rest
of TinyGo's sync.Map.

Author: jakebailey

src/sync/map.go

@@ -82,3 +82,34 @@ func (m *Map) Swap(key, value any) (previous any, loaded bool) {
 	m.m[key] = value
 	return
 }
+
+// CompareAndSwap swaps the old and new values for an existing key if the value
+// stored in the map is equal to old.
+func (m *Map) CompareAndSwap(key, old, new any) (swapped bool) {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+	if m.m == nil {
+		return false
+	}
+	value, ok := m.m[key]
+	if !ok || value != old {
+		return false
+	}
+	m.m[key] = new
+	return true
+}
+
+// CompareAndDelete deletes the entry for key if its value is equal to old.
+func (m *Map) CompareAndDelete(key, old any) (deleted bool) {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+	if m.m == nil {
+		return false
+	}
+	value, ok := m.m[key]
+	if !ok || value != old {
+		return false
+	}
+	delete(m.m, key)
+	return true
+}