fix: handle matrix.to prefix when starting chat

- remove leading matrix.to beginning from content of the start chat
  matrix.to text field in order to allow simply pasting matrix.to links

Signed-off-by: TheOneWithTheBraid <the-one@with-the-braid.cf>

lib/pages/new_private_chat/new_private_chat.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 
 import 'package:device_info_plus/device_info_plus.dart';
 import 'package:flutter_gen/gen_l10n/l10n.dart';
@@ -27,11 +28,18 @@ class NewPrivateChatController extends State<NewPrivateChat> {
 
   bool _hideFab = false;
 
+  // remove leading matrix.to from text field in order to simplify pasting
+  final List<TextInputFormatter> removeMatrixToFormatters = [
+    FilteringTextInputFormatter.deny(NewPrivateChatController.prefix),
+    FilteringTextInputFormatter.deny(NewPrivateChatController.prefixNoProtocol),
+  ];
+
   bool get hideFab => _hideFab;
 
   static const Set<String> supportedSigils = {'@', '!', '#'};
 
   static const String prefix = 'https://matrix.to/#/';
+  static const String prefixNoProtocol = 'matrix.to/#/';
 
   void setHideFab() {
     if (textFieldFocus.hasFocus != _hideFab) {

lib/pages/new_private_chat/new_private_chat_view.dart

@@ -83,10 +83,11 @@ class NewPrivateChatView extends StatelessWidget {
                   focusNode: controller.textFieldFocus,
                   onFieldSubmitted: controller.submitAction,
                   validator: controller.validateForm,
+                  inputFormatters: controller.removeMatrixToFormatters,
                   decoration: InputDecoration(
                     labelText: L10n.of(context)!.typeInInviteLinkManually,
                     hintText: '@username',
-                    prefixText: 'matrix.to/#/',
+                    prefixText: NewPrivateChatController.prefixNoProtocol,
                     suffixIcon: IconButton(
                       icon: const Icon(Icons.send_outlined),
                       onPressed: controller.submitAction,