Compose UI for native Linux

[Thomas-Vos]

This PR is just to gather some feedback, definitely not ready to merge. A lot of code is missing or just copied from other platforms. Which has to be implemented with probably something like Wayland. Preferably not breaking usage on embedded systems without Wayland if possible.

Depends on:

• Add linuxArm64 target skiko#1051
• Move Synchronization.nativeMain.kt to darwinMain source set #2006
• Add linuxMain source set #2007

To build this branch use a local version of skiko containing JetBrains/skiko#1051. For EGL this is needed as well:

• Enable EGL skia-pack#68
• Add support for EGL skiko#1052

[Thomas-Vos]

Many features in this PR are not implemented (this is just one random example). I am afraid that using wayland code here could break it for non-wayland apps.

My use case is using Compose on an embedded system which is not using wayland but manufacturer specific APIs for most (windowing) features. I need to implement some of these functions with manufacturer-specific code, which of course can never be merged into compose.

As this is an expect/actual (like almost everywhere), I do not know of an easy way to pull out the wayland code into a separate module. Ideally a user like me can provide their own implementation for the windowing features. Or maybe multiple separate modules (one for wayland, etc). Any ideas what would work best?