bug: backspace creates newline on mobile (Android, Firefox- and Chromium derivatives)

Describe the bug

• On Chromium-based browsers (tested Google Chrome and Cromite), the backspace inserts a newline rather than deleting the line.
• On Firefox-based browsers (tested Mozilla Firefox and IronFox), the backspace is unresponsive, rather than deleting the line.

I have confirmed this with the AOSP keyboard, in addition to FUTO keyboard and FlorisBoard.

Notably, this does not happen on the first line, but does from the second line onwards, nor does it happen if there aren't any characters on any line.

Two videos trying in clean, newly installed Chrome and Firefox with all three above mentioned keyboards.

https://github.com/user-attachments/assets/e32756c8-9a12-4d61-9962-c29e293c0d72
https://github.com/user-attachments/assets/3d720c99-811d-4180-8fdc-787063fcc4b9

I did notice https://github.com/TypeCellOS/BlockNote/issues/1725, which was closed as not reproducible three months ago and was unsure whether to comment on that issue or create a new one. So here goes nothing...

To Reproduce

• Open https://www.blocknotejs.org/examples/basic/minimal in a Chromium or Firefox based browser
• Type >= 1 characters
• Press enter to create a newline
• Press backspace to try to delete the line
• Observe it either creates a newline (Chromium) or does nothing (Firefox), either way not the expected behavior of deleting the line.

Misc

• Node version: demo website
• Package manager: demo website
• Browser: Firefox- and Chromium-derivatives on Android
• I'm a sponsor and would appreciate if you could look into this sooner than later 💖