Support macOS .icon format

[ErnSur]

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Description

closes #7530

In order to support the macOS Tahoe icon styles (dark, clear, tinted) a new icon format must be used for the app icon asset.
In this PR I updated the electron-builder to a version that supports the.icon assets and replaced the legacy .icns asset with the new .icon one.

The .icon file was taken from the Signal iOS repository

New icons with light and dark style settings:

[cbrnr]

Could you show a screenshot of the new icon in both light and dark mode, preferably next to some other macOS icons like Finder, Safari, Terminal, etc.? I'm asking because I manually replaced the Signal app icon with the one from iOS (right-click on the app, Get info, drag new icon onto the previewed icon), and it does not look good (it is too large compared to the others):

Maybe that's just because manually replacing doesn't work, but I would still double-check if the new icon looks good, or if the iOS icon has to be adapted in some way.

[ErnSur]

Could you show a screenshot of the new icon in both light and dark mode

I updated the PR description with two screenshots.

@ayumi-signal Is this PR likely to be merged anytime soon?

[ayumi-signal]

Hi, sorry for the delay. We've been trying to update electron-builder but with the last attempt there was an issue with the electron/universal dependency. Once we're able to update electron-builder then we can fix the icon.

[ErnSur]

Hi, sorry for the delay. We've been trying to update electron-builder but with the last attempt there was an issue with the electron/universal dependency. Once we're able to update electron-builder then we can fix the icon.

Is there an issue/PR where this problem is described in more detail?

[winzig]

Yes is there an issue we can follow for the underlying blocking issue you described @ayumi-signal?