After commit 3e5aa212d5 the Slint DLLs
aren't placed in the `bin/` directory by default anymore. Since the
tutorial builds Slint as an external sub-project, it is entirely
isolated and the CMAKE_*_OUTPUT_DIRECTORY variables do not propagate. On
macOS and Linux, the program still runs due to rpath. On Windows, the
instructions said to put `bin` into `%PATH%`, but that doesn't work
anymore, the dll is now in `_deps/slint-build`.
Instead of adjusting `%PATH%`, this change adjusts the documentation to
recommend the use of a custom command on Windows using
$<TARGET_RUNTIME_DLLS:tgt> to copy the DLL across. This is guarded with
WIN32 due to https://gitlab.kitware.com/cmake/cmake/-/issues/23543 ,
where the proposed solution requires CMake 3.26 (not released yet).
We used to have SLINT_FEATURE_BACKEND_GL_ALL, but when we introduced the
renderer and event loop distinction in the features, we removed the "all" suffix from
the event loop that includes x11 and wayland support.
Split backend-gl-* into eventloop-winit-* and renderer-femtovg.
The old feature names are still available.
For consistency eventloop-qt and renderer-qt are aliases for backend-qt.
This is only required for dependencies of slint-build and xtask.
So this is not enforced yet and will still work with 1.56 with
for C++ or when not using slint-build.
