move gotd fork into repo. (#111)

- update to latest telegram layer
- remove some references to fields in tg.Entities that don't exist in
the schema
- originally added here:
https://github.com/beeper/td/commit/820929062a2ba0104397bc01235ab58a9cff780e
  - referenced here
-
https://github.com/mautrix/telegramgo/commit/124f0967ed195b5a380c9bd02e170ada9710dde3
-
https://github.com/mautrix/telegramgo/commit/4205047aab2e0639217148b5d125bfaab668bd8e

pkg/gotd/tmap/constructor.go

@@ -0,0 +1,39 @@
+package tmap
+
+import "go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+
+// Constructor maps type id to type constructor.
+type Constructor struct {
+	types map[uint32]func() bin.Object
+}
+
+func (c *Constructor) add(mapping map[uint32]func() bin.Object) {
+	// Probably it is good place to catch collisions, but
+	// ignoring for now.
+	for k, v := range mapping {
+		c.types[k] = v
+	}
+}
+
+// New instantiates new value for type id or returns nil.
+func (c *Constructor) New(id uint32) bin.Object {
+	if c == nil || len(c.types) == 0 {
+		return nil
+	}
+	fn := c.types[id]
+	if fn == nil {
+		return nil
+	}
+	return fn()
+}
+
+// NewConstructor merges mappings into Constructor.
+func NewConstructor(mappings ...map[uint32]func() bin.Object) *Constructor {
+	c := &Constructor{
+		types: map[uint32]func() bin.Object{},
+	}
+	for _, m := range mappings {
+		c.add(m)
+	}
+	return c
+}