"Pressed" detection bugged after unfocusing in game in WASM

## Bevy version
0.13

## \[Optional\] Relevant system information
- Windows 10
- Firefox
- Chrome

## What you did
I held down a button then unfocused the window.

## What went wrong
The button remained held down according to ButtonInput "pressed" even when I released it. Refocusing the window does not fix this, but refocusing then pressing and releasing does.

## Additional information
Tested in both Firefox and Chrome with similar behaviors.

Start by reproducing the issue in a WASM build in Firefox and Chrome, using the ButtonInput "pressed" state and the focus-loss sequence described. Trace how input state is handled when the game window loses and regains focus; done when releasing the button after refocusing clears the pressed state without requiring another press.

Written by the indexing model from the issue text.