Use text entered before selecting an image to send as image caption

### Your use case

#### What would you like to do?

I would like to use my text that I entered in the composer as an image caption.

#### Why would you like to do it?

Convenience. Because I forget to select the image before writing a caption or because I'm writing a message and then deciding to send an supporting image.

#### How would you like to achieve it?

- If I entered text that I did not send as a message yet (the composer is not empty) and then select an image, I want the entered text from before to be used as the image caption - meaning that the text is copied and used to pre-fill the image caption text input.
- If I then send the image with that caption, it should be removed from the message composer where I first added it
- If I cancel sending the image, eg. by using the back button, the text should not be lost, but instead it should still be in the message composer where I first entered it
- If I only entered text for the image caption after selecting an image, that should not be copied to the message composer

### Have you considered any alternatives?

_No response_

### Additional context

I want to have an familiar interaction flow - other apps, like Signal and Whatsapp also behave as described.

### Are you willing to provide a PR?

No