NeoVim UI implemented in gtk4/vala

The project is abandoned in favour of neovim-sdl2.

I need an easy deployable low latency UI for NeoVim in Windows. It should be both simple and flexible. Turns out, it's quite easy to code after experiments with SpyUI.

• Calculate width, height from the window size and chosen font
• Redraw only changed parts of the screen, use an offscreen surface like in gtk4-demo
• Improve redrawing by combining adjacent cells with the same hl_id
• Test MinGW build
• Setup GitHub actions to build for Win32
• Cursor shapes
• Use pango for text layout
• Log to a file instead of stdout
• Properly close the editor when the window is about to be closed
• Allow selecting GUI font
• Mouse support
• Fast zoom with mouse wheel
• Automatic testing
• Make redrawing atomic with flush
• Get rid of console in windows
• Handle special keys like arrows, functional keys
• Handle the rest of highlight attributes
• Handle errors and failures
• Consider externalizing popup menus to add scrollbars
• Configuration of fonts and behaviour tweaking (consider using lua)
• Change mouse pointer on busy_start/busy_stop notifications
• Create window after neovim has been launched and initialized to avoid white flash during startup
• Setup automatic releases (win32, appimage)
• Track mode_info