Allow disabling Markdown Formatting

### Your use case

#### What would you like to do?
Add a button like Element Client.


#### Why would you like to do it?
The Markdown format causes the message text to be scrambled.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

### Are you willing to provide a PR?

No

No files or tests are named. Start by inspecting the message composer in this Kotlin/Jetpack Compose Android app and compare the formatting toggle shown in Element Client. Done means users can disable Markdown formatting with a visible button and messages retain the intended text when that option is off.

Written by the indexing model from the issue text.