Release 8.4.0

[danirabbit]

Todo:

• Fix blurry icons when running with fractional scaling #2665
• wayland: Add make_modal protocol method #1974
• WindowStateSaver: validate saved window position before placing #2611
• PropertyTarget: remove transitions on gesture start #2625
• old-icon-groups=false?

[leolost2605]

Some more candidates:

• Maybe Support keyboard navigation over multiple monitors in multitasking view #2536 since it fixes two annoying regressions for keyboard users
• Since we have Enable 'scale-monitor-framebuffer' by default #2660 now maybe Fix blurry icons when running with fractional scaling #2665? Would also unblock using that in the other two places where we have blurry icons (window icon and resize)

[danirabbit]

@leolost2605 @lenemter I don't feel qualified to review #2536, but this release is blocking some other releases because of the modal protocol. Would it be okay to get this one out there and bump that to the next gala release?