Reply to a poll (#1848)

<!-- Please read [CONTRIBUTING.md](https://github.com/vector-im/element-x-android/blob/develop/CONTRIBUTING.md) before submitting your pull request -->
 
## 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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We have screenshot tests in the project, so attaching screenshots to a PR is not mandatory, as far as there
is a Composable Preview covering the changes. In this case, the change will appear in the file diff.
Note that all the UI composables should be covered by a Composable Preview.

Providing a video of the change is still very useful for the reviewer and for the history of the project.

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## Tests

<!-- Explain how you tested your development -->

- Step 1
- Step 2
- Step ...

## Tested devices

- [ ] Physical
- [ ] Emulator
- OS version(s):

## Checklist

<!-- Depending on the Pull Request content, it can be acceptable if some of the following checkboxes stay unchecked. -->

- [ ] 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
- [ ] Pull request includes screenshots or videos if containing UI changes
- [ ] Pull request includes a [sign off](https://matrix-org.github.io/synapse/latest/development/contributing_guide.html#sign-off)
- [ ] You've made a self review of your PR

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