* Add plain text representation of messages.
This is used in the room list as the last message in a room, in the message summary when a message is selected, in the 'replying to' block, in the 'replied to' block in a message in the timeline, and in notifications.
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## Type of change
- [x] Feature
- [ ] Bugfix
- [ ] Technical
- [ ] Other :
## Content
Polls can now be replied to.
## Motivation and context
User story: https://github.com/vector-im/element-meta/issues/1976
## Screenshots / GIFs
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## Tests
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## Tested devices
- [ ] Physical
- [ ] Emulator
- OS version(s):
## Checklist
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- [ ] 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/vector-im/element-x-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-x-android/blob/develop/CONTRIBUTING.md#changelog
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- Voice messages can be scrubbed (i.e. seeked to) even when they have not been played yet..
- The progress bar is displayed also when paused.
- Multiple voice messages can keep their state when paused.
- Tries to adhere as much as possible at the detailed "green cursor" behavior in the story (but might not be 100% compliant).
Story: https://github.com/vector-im/element-meta/issues/2113
* Integrate mentions in the composer:
- Add `MentionSpanProvider`.
- Add custom colors needed for mentions.
- Use the span provider to render mentions in the composer.
- Allow selecting users from the mentions suggestions to insert a mention.
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Co-authored-by: ElementBot <benoitm+elementbot@element.io>
