Add freedesktop compliant appstream & metainfo

[Doomsdayrs]

Validated to match requirements set by freedesktop via desktop-file-check and flatpak run org.freedesktop.appstream-glib validate rs.ruffle.Ruffle.metainfo.xml.

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Related: https://github.com/ruffle-rs/ruffle/issues/9220

[Doomsdayrs]

~~Note, If the metainfo file is accepted upstream, it is expected to be automatically updated by upstream as well with each release of Ruffle (or pre-release with the current model).~~

[torokati44]

So, do you think the <release version="nightly-2023-05-26" date="2022-05-26"/> issue could be automated away somehow, so that it's not hardcoded in the repo, and doesn't need to be updated - rather, filled out as part of the flatpak build process? Perhaps https://github.com/ruffle-rs/ruffle/blob/master/web/packages/core/tools/set_version.js can give some inspiration - it could even be used as is, and then copying the version over from the .json to the .xml somehow?

[torokati44]

Also, by this time, our menu has gained some new items, and the launcher is an "advanced open dialog" now, so could you please update the screenshots? Sorry for dragging this out for so long...

[torokati44]

filled out as part of the flatpak build process

See for example how the AUR package does it: https://github.com/ruffle-rs/ruffle/blob/master/.github/workflows/release_nightly.yml#L516-L531

I think a similar solution (in the "recipe" to build it) would be fine here as well, as part of: https://github.com/flathub/flathub/pull/4179

[Doomsdayrs]

Also, by this time, our menu has gained some new items, and the launcher is an "advanced open dialog" now, so could you please update the screenshots? Sorry for dragging this out for so long...

Done!

[jh-devv]

I saw a Mastodon post about this, does the GitHub actions thing still need help? I would be open to help!

[Doomsdayrs]

I saw a Mastodon post about this, does the GitHub actions thing still need help? I would be open to help!

Yes!

[jh-devv]

I saw a Mastodon post about this, does the GitHub actions thing still need help? I would be open to help!

Yes!

Good, I'll look into that when I have time! 🥳

[kjarosh]

Refreshed this PR a bit, most notable changes:

• updated screenshots (ensured that window shadow and rounded corners are included as per the guidelines),
• updated URLs (to conform to appstream spec),
• updated the update_contact to our official email address and made the developer name more human-friendly,
• removed list of releases (we will have to figure this out in the future — either update them automatically each stable release or fill them when building the flatpak).

To do:

• [x] add light theme screenshots after https://github.com/ruffle-rs/ruffle/pull/17179 (as per the quality guidelines),
• [x] update screenshots after https://github.com/ruffle-rs/ruffle/pull/17042,
• [x] update the description — currently a lot of it mentions the web version (which the desktop application has little to do with).

[kjarosh]

Thank you to all the contributors!