Fix long click not working for media timeline items

[jmartinesp]

Content

Add nullable onContentClick and onLongClick callbacks for the media timeline item content, so they can register custom actions for these user interactions.

Motivation and context

https://github.com/element-hq/element-x-android/pull/3864 introduced a regression that prevented long click from working on media and location items unless they had a caption.

Screenshots / GIFs

No screenshot changes, I hope.

Tests

On a room, long press on:

• An image/video item.
• An image/video item with captions.
• A sticker.
• A location item.

You can double check other items too, but these should be the ones that changed.

Tested devices

• [x] Physical
• [ ] Emulator
• OS version(s): 14

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
• [x] Pull request is based on the develop branch
• [x] 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
• [x] You've made a self review of your PR

[github-actions[bot]]

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[sonarcloud[bot]]

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 SonarQube Cloud

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 61.90476% with 8 lines in your changes missing coverage. Please review.

Project coverage is 82.86%. Comparing base (1be7993) to head (9e9aec9). Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
...imeline/components/TimelineItemGroupedEventsRow.kt	0.00%	4 Missing :warning:
...ssages/impl/timeline/components/TimelineItemRow.kt	50.00%	0 Missing and 1 partial :warning:
...e/components/event/TimelineItemEventContentView.kt	66.66%	1 Missing :warning:
...meline/components/event/TimelineItemStickerView.kt	0.00%	0 Missing and 1 partial :warning:
...timeline/components/event/TimelineItemVideoView.kt	0.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #3879 +/- ## =========================================== - Coverage 82.87% 82.86% -0.01% =========================================== Files 1785 1785 Lines 45100 45106 +6 Branches 5324 5326 +2 =========================================== + Hits 37377 37379 +2 - Misses 5857 5858 +1 - Partials 1866 1869 +3 ```

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