Implement MSC2530

[surakin]

Depends on matrix-org/matrix-rust-sdk#3171
Fixes #2521

Type of change

• Feature
• Bugfix
• Technical
• Other :

Content

Show body as image caption, per MSC 2530

Motivation and context

Caption as a different message doesn't look this good

Screenshots / GIFs

Tests

• Send an image using with a bridge/client with body as caption enabled (mautrix-whatsapp for example)
• See how the image is displayed with caption instead of in a separate message.

Tested devices

• Physical
• Emulator
• OS version(s):

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 includes a new file under ./changelog.d. See https://github.com/element-hq/element-x-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

[github-actions]

Thank you for your contribution! Here are a few things to check in the PR to ensure it's reviewed as quickly as possible:

• Your branch should be based on origin/develop, at least when it was created.
• There is a changelog entry in the changelog.d folder with the Towncrier format.
• The test pass locally running ./gradlew test.
• The code quality check suite pass locally running ./gradlew runQualityChecks.
• If you modified anything related to the UI, including previews, you'll have to run the Record screenshots GH action in your forked repo: that will generate compatible new screenshots. However, given Github Actions limitations, it will prevent the CI from running temporarily, until you upload a new commit after that one. To do so, just pull the latest changes and push an empty commit.

[surakin]

Not convinced about how that column looks like, but it's sunday so I'll keep trying later

[surakin]

The 'Record Screenshots' action seems be failing but I don't see any error related to this change on its log 🤔

[jmartinesp]

Thanks for the changes! I'll merge it to a branch of mine where I can tweak these changes a bit so they fit a bit better our layout.