android: Added android_usecase kwargs to executable

[sp1ritCS]

This is the idea I've came up with in regards to #13758

It doesn't do anything regarding application glue right now, as I'm unsure if and how to implement it, but I thought about it some more and belive having it would simplify things quite a bit.

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By setting android_usecase to application, the executable gets actually built as a shared library instead of an executable. This makes it possible to use an application within an android application process.

https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/7555/

[jpakkane]

Could you not already do this with the build_target function?

[sp1ritCS]

Perhaps. However my goal is to have a builder tool that you can just point at a meson project to create an apk from.

While you still have to modify your meson sources and to add the android_usecase, it seems less invasive than doing having users switch their excecutables to build_target(target_type: host_machine.os() == android ? 'shared_module' : 'executable', ...), especially given that they will have to add the android glue dependency too (declaring a link_whole dependency with it and adding it does seem to work within meson, not sure why cmake didn't like it)

What about adding a excecutable function to the gnome module that has the same prototype as a normal executable but that creates a library linked against the glue dependency if host_machine == 'android'?