The chat / commands their autocomplete stays present and reappears after being accepted

### Steps to reproduce

1. The user starts his chat message with for example /plain
2. The user presses enter to sort of accept the command and this hides the autocomplete for it
3. The user continues with typing his message

### Outcome

#### What did you expect?
- After accepting the autocomplete for the command used, the autocomplete remains hidden while typing outside of the / command itself.
- Extra feature: have a command that is accepted appear marked in the chat input to visually show it is an activated command (space after the / command was used or the autocomplete being accepted as triggers).

#### What happened instead?
- Pressing enter or esc on the autocomplete hides it, but any keypress makes it reappear again even after we're past writing the command itself (as our input focus is separated from the command itself by a space and further text).

### Operating system

_No response_

### Browser information

_No response_

### URL for webapp

_No response_

### Application version

_No response_

### Homeserver

_No response_

### Will you send logs?

No

Start by reproducing the issue in the web app's chat input with a slash command such as /plain, then trace the command autocomplete behavior after Enter or Escape and while typing text after a space. Done means accepting or dismissing the command keeps autocomplete hidden outside the command itself, with the expected behavior covered by an appropriate test.

Written by the indexing model from the issue text.