When pasting onto a non-collapsed selection, the selection should collapse. Confirmed on native Mac, Windows, Android and iOS. I'd be shocked if Linux isn't the same too.

If you paste with the keyboard while the cursor is offscreen, the cursor should be scrolled into view, but it isn't.

Steps to reproduce

1. Run any app with a text field, such as the one below.
2. Enter some text, like "asdf".
3. Copy any text.
4. Make any selection of length > 0.
5. Paste (using the keyboard or using the toolbar).

Expected: The cursor ends up collapsed at the end of the pasted text.
Actual: The pasted text is selected.

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Flutter Demo'),
        ),
        body: const Center(
          child: TextField(),
        ),
      ),
    );
  }
}

Related: #98604 (comment)