Editor state fixture and preview improvement

[bmarty]

Content

Improve the code for the state composer fixture and for the preview, and add content in the existing preview for the TextComposer.

Motivation and context

Preparatory work for

• send media caption
• Emptiing the composer when editing the message allow to record a voice message #3756

Screenshots / GIFs

Tests

• No functional change in this PR, just working around Preview, which is sort of non production code.

Tested devices

• NA

Checklist

• Changes have been tested on an Android device or Android emulator with API 23
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com/element-hq/element-x-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request title will be used in the release note, it clearly define what will change for the user
• 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

[github-actions]

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[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud