RichTextEditor code block editing artefacts

[stefanceriu]

Try editing a message that only contains a codeblock

1) Cancelling the editing leaves the cursor in the wrong position. Entering a character fixes it

2) Delete everything within the code block before cancelling the edit. The codeblock background box remains in the composer

[alfogrillo]

2. should be fixed by https://github.com/matrix-org/matrix-rich-text-editor/pull/829

[Velin92]

duplicate of https://github.com/element-hq/element-x-ios/issues/2656