[Rich text editor] Fix design and spacing of rich text editor

[jonnyandrew]

Type of change

• Feature
• Bugfix
• Technical
• Other :

Content

Improve design and spacing of the rich text editor.

Minor changes to

• position of input field relative to buttons
• spacing around attachments button
• spacing around send button
• selectable backgrounds

Motivation and context

https://element-io.atlassian.net/browse/PSU-994

Screenshots / GIFs

	Before	After
Empty input, formatting disabled
Empty input, formatting enabled
Text in input, formatting disabled
Text in input, formatting enabled

Tests

1. Enable rich text editor (via labs)
2. Navigate to a room
3. Enable text formatting (via the attachment menu)
4. Check design
5. Disable text formatting (via the attachment menu)
6. Check design

Tested devices

• Physical
• Emulator
• OS version(s): Android 13

Checklist

• Changes has been tested on an Android device or Android emulator with API 21
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com./vector-im/element-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request includes a new file under ./changelog.d. See https://github.com./vector-im/element-android/blob/develop/CONTRIBUTING.md#changelog
• Pull request includes screenshots or videos if containing UI changes
• Pull request includes a sign off
• You've made a self review of your PR
• If you have modified the screen flow, or added new screens to the application, you have updated the test UiAllScreensSanityTest.allScreensTest()

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

0.0% Coverage
0.0% Duplication

[mnaturel]

LGTM.