Use unicode icons for entry icons

[davidfraser]

Use unicode icons to give a wider range of options for entry icons

By default KeePassXC shows a limited list of about 70 default icons when choosing the icon for an entry.
Users can then supplement these by selecting custom icons. This is great when used together with the favicon selector for a website. But these icons all need to be added to the database, and other than a favicon it requires a little effort to select and download an icon
Unicode now includes a wide variety of emojis that are specified merely by a single code point. Sites like unicode.party allow searching these emojis to quickly find one with a given theme.
I think providing an option to use these emojis as the icon would be great.

Examples

The icon editor could show:

[ ] Use default icon
(default icons)
[ ] Use unicode icon
(optional text box to search for icon, list of icons)
[ ] Use custom icon
(custom icons)

The text box could like like it does in unicode party:

Context

I often find the set of icons available limiting when choosing for example pictures for people's security codes for an alarm

[droidmonkey]

These should be implemented together: #7159

[droidmonkey]

https://github.com/svgmoji/svgmoji

I personally like Noto and Twemoji. OpenMoji is too sketch art for our overall UI theme.

[phoerious]

Do we need a library? Most systems should support emoji out of the box if you just display the code points.

[droidmonkey]

Just preparing myself

[droidmonkey]

https://github.com/AmirHosseinCH/EmojiPicker

[phoerious]

If possible, we should use the system's emoji picker. At least macOS offers one.

[droidmonkey]

Windows does as well, will investigate the api call necessary. Edit: looks like you need to simulate keypresses to show it. Luckily we do that rather well.