[feature] Account alias / move API + db models (#2518)

* [feature] Account alias / move API + db models

* go fmt

* fix little cherry-pick issues

* update error checking, formatting

* add and use new util functions to simplify alias logic

internal/util/deduplicate.go

@@ -0,0 +1,63 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package util
+
+// Deduplicate deduplicates entries in the given slice.
+func Deduplicate[T comparable](in []T) []T {
+	var (
+		inL     = len(in)
+		unique  = make(map[T]struct{}, inL)
+		deduped = make([]T, 0, inL)
+	)
+
+	for _, v := range in {
+		if _, ok := unique[v]; ok {
+			// Already have this.
+			continue
+		}
+
+		unique[v] = struct{}{}
+		deduped = append(deduped, v)
+	}
+
+	return deduped
+}
+
+// DeduplicateFunc deduplicates entries in the given
+// slice, using the result of key() to gauge uniqueness.
+func DeduplicateFunc[T any, C comparable](in []T, key func(v T) C) []T {
+	var (
+		inL     = len(in)
+		unique  = make(map[C]struct{}, inL)
+		deduped = make([]T, 0, inL)
+	)
+
+	for _, v := range in {
+		k := key(v)
+
+		if _, ok := unique[k]; ok {
+			// Already have this.
+			continue
+		}
+
+		unique[k] = struct{}{}
+		deduped = append(deduped, v)
+	}
+
+	return deduped
+}