Replace QtGreet with a QML-based greeter for greetd

[UriHerrera]

I've encountered some issues while customizing the QtGreet theme in Nitrux—specifically, the limitations in QtWidgets and QSS.

I tried to match the Waybar look we're using, but it didn't turn out well. As I alluded to before, QSS has limitations and doesn't implement all CSS properties; for example, I can't replicate the shadow behind the islands.

Additionally, I can't seem to use an image for the power button, so I had to use an emoji, which still didn't scale correctly.

The text also seemed strangely smaller, even though it was the same size and font as in Waybar.

There were additional limitations caused by QtGreet itself, such as:

• The Caps Lock indicator cannot be themed due to paintEvent limitations in the C++ code.
• C++ source code has hardcoded the height of widgets (input fields and buttons) to 27px.
• The size of the user avatar is also hardcoded to 72px. Increasing the container size does not scale the image.
• No support for QML.

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That said, there are no existing QML greeters for greetd at the time of writing.

[UriHerrera]

I've started working on a QML greeter, https://github.com/Nitrux/qmlgreet. I might change the name later.

[UriHerrera]

Here's in its final form. It's also successfully integrated into the distribution.