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/gen/make_errors.go

@@ -0,0 +1,66 @@
+package gen
+
+import (
+	"sort"
+	"strings"
+
+	"github.com/gotd/getdoc"
+)
+
+// errCheckDef is helper for checking errors.
+type errCheckDef struct {
+	// Name of check without "Is" prefix.
+	Name string
+	// Type of error.
+	Type string
+}
+
+func (Generator) errDef(err getdoc.Error) errCheckDef {
+	var parts []string
+	for _, p := range strings.Split(err.Type, "_") {
+		switch p {
+		case "X", "*", "%d":
+			continue
+		default:
+			p = strings.ReplaceAll(p, "%d", "")
+			parts = append(parts, p)
+		}
+	}
+	var partsLower []string
+	for _, p := range parts {
+		partsLower = append(partsLower, strings.ToLower(p))
+	}
+	return errCheckDef{
+		Name: pascalWords(partsLower),
+		Type: strings.Join(parts, "_"),
+	}
+}
+
+// makeErrors created go definitions for possible errors.
+func (g *Generator) makeErrors() {
+	if g.doc == nil {
+		return
+	}
+
+	// For each unique error Type, create error check definition.
+	// Like IsNeedMigration(err) function.
+	seen := make(map[string]struct{})
+	for _, m := range g.structs {
+		for _, e := range m.Errors {
+			d := g.errDef(e)
+
+			if _, ok := seen[d.Type]; ok {
+				continue
+			}
+			seen[d.Type] = struct{}{}
+
+			g.errorChecks = append(g.errorChecks, d)
+		}
+	}
+
+	// Ensure error order.
+	sort.SliceStable(g.errorChecks, func(i, j int) bool {
+		a, b := g.errorChecks[i], g.errorChecks[j]
+		return a.Type < b.Type
+	})
+}