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/telegram/message/entity/token_test.go

@@ -0,0 +1,38 @@
+package entity
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+)
+
+func TestToken_Apply(t *testing.T) {
+	var (
+		a = require.New(t)
+		b = &Builder{}
+	)
+	_ = b.WriteByte('a')
+	tok := b.Token()
+	a.Equal(1, tok.UTF8Offset())
+	a.Equal(1, tok.UTF16Offset())
+
+	a.Zero(tok.UTF8Length(b))
+	a.Zero(tok.UTF16Length(b))
+	a.Empty(tok.Text(b))
+
+	text := "abc🏳"
+	_, _ = b.WriteString(text)
+	a.Equal(text, tok.Text(b))
+	utf16Len := ComputeLength(tok.Text(b))
+
+	a.Equal(b.message.Len()-tok.UTF8Offset(), tok.UTF8Length(b))
+	a.Equal(utf16Len, tok.UTF16Length(b))
+
+	tok.Apply(b, Bold())
+	a.Equal(1, b.EntitiesLen())
+	e, ok := b.LastEntity()
+	a.True(ok)
+	a.Equal(&tg.MessageEntityBold{Offset: 1, Length: utf16Len}, e)
+}