By default, Flutter web uses the browser's built-in context menu.

<img width="200" src="https://github.com/flutter/flutter/assets/389558/990f99cb-bc38-40f1-9e88-8839bc342da5" />

As of [recently](https://github.com/flutter/engine/pull/38682), it's possible to use a Flutter-rendered context menu like the other platforms.

```dart
void main() {
  runApp(const MyApp());
  BrowserContextMenu.disableContextMenu();
}
```

But there is a bug (https://github.com/flutter/flutter/issues/129692) that the Paste button is missing and never shows up.

<img width="284" alt="Screenshot 2023-08-07 at 2 39 03 PM" src="https://github.com/flutter/flutter/assets/389558/f632be25-28b1-4e2e-98f7-3bb443f077df">

The reason why it's missing is that Flutter first checks if there is any pasteable text on the clipboard before deciding to show the Paste button using the `hasStrings` platform channel method, but that was never implemented for web ([original hasStrings PR](https://github.com/flutter/flutter/pull/87678)).

So let's just implement hasStrings for web?  No, because Chrome shows a permissions prompt when the clipboard is accessed, and there is [no browser clipboard API](https://developer.mozilla.org/en-US/docs/Web/API/Clipboard_API) to avoid it.  The prompt will show immediately when the EditableText is built, not just when the Paste button is pressed.

<img width="200" src="https://github.com/flutter/flutter/assets/389558/5abdb160-1b13-4f1a-87e1-4653ca19d73e" />

### This PR's solution

Instead, before implementing hasStrings for web, this PR disables the hasStrings check for web.  The result is that users will always see a paste button, even in the (unlikely) case that they have nothing pasteable on the clipboard.  However, they will not see a permissions dialog until they actually click the Paste button.  Subsequent pastes don't show the permission dialog.

<details>

<summary>Video of final behavior with this PR</summary>

https://github.com/flutter/flutter/assets/389558/ed16c925-8111-44a7-99e8-35a09d682748

</details>

I think this will be the desired behavior for the vast majority of app developers.  Those that want different behavior can use hasStrings themselves, which will be implemented in https://github.com/flutter/engine/pull/43360.

### References

Fixes https://github.com/flutter/flutter/issues/129692
Engine PR to be merged after this: https://github.com/flutter/engine/pull/43360