feat: add subtitle toggle hotkey

[schembriaiden]

Pull Request Description

This pull request introduces a new "toggle subtitles" hotkey feature to the video player, allowing users to quickly enable or disable subtitles using a keyboard shortcut. The implementation includes localization, hotkey mapping, and logic for toggling subtitles, including handling multiple subtitle tracks and remembering the user's last selection.

New Subtitle Toggle Feature:

• Added a new toggleSubtitles hotkey to the VideoHotKeys enum, mapped by default to the "T" key (LogicalKeyboardKey.keyT).
• Implemented the _toggleSubtitles method in _DesktopControlsState to handle toggling subtitles on/off, supporting both single and multiple subtitle tracks and remembering the last selected subtitle.
• Integrated the new hotkey into the video player controls so pressing the hotkey triggers subtitle toggling.

Localization:

• Added the toggleSubtitles string to the English localization file (app_en.arb) for display in the UI and settings.
• Updated the VideoHotKeys label mapping to include the new toggleSubtitles key for proper display in settings menus.

Codebase Maintenance:

• Added the necessary import for media_streams_model.dart to support subtitle toggling logic.
• Introduced a _lastSelectedSubtitleIndex state variable to remember the user's last subtitle choice across toggles.

Logic is as follow:

Press toggle:

1. If there is only 1 type of subtitle it just uses it
2. If there is multiple subtitle types:
   1. First time it asks you to select the one you want
   2. After it keeps using the same one.

Issue Being Fixed

Resolves #957

Screenshots / Recordings

Tested On

• Android
• Android TV
• iOS
• Linux
• Windows
• macOS
• Web

Checklist

• If a new package was added, did you ensure it works for all supported platforms? Is the package well maintained
• Check that any changes are related to the issue at hand.

[PartyDonut]

I'm not entirely sure about the logic here. Does it make sense for the user to press the "toggle" button to all of a sudden ask what subtitles they want to toggle in-between?

Would it make more sense to just do nothing if the subtitles are already disabled and only allow toggling when a subtitle is enabled?

No strong opinion on my end just thinking out loud.

[schembriaiden]

I am not against the idea, but I think this might lead users to open issues on GitHub saying that the toggle key is not working, when in fact it would be working. Then from experience I know that most people don't check previous issues before opening one which would lead to a bunch of duplicate issues regarding this.

[PartyDonut]

Silly question but why T? Youtube for instance uses the C button for "Captions"

[schembriaiden]

I was initially going to go with C to mirror Youtube's logic, but since the request suggested T I just went with that, we can do whatever I don't mind.