macOS seems to require that we declare the extensions we want to
consider those files to be droppable on the window. Additionally this is
of course needed to show melonDS as a selectable option in the "Open
with" menu and such.
Setting LSHandlerRank to Alternate appears to stop it from suggesting
melonDS as a primary handler for a file type, so we set this for GBA
ROMs and archives as the user would most likely want them always to be
associated with a more relevant app.
According to the Qt documentation we should have this for proper
high-DPI support on macOS. Whether or not it's still relevant I'm not
sure, but if it isn't it might at least help on older macOS or Qt.
These changes modernize the CMake build system to (hopefully) match newer best practices
* Library linking is simpler and more automatic because of using imported targets
* Multi-configuration builds should be supported (Ninja Multi-Config, Visual Studio, etc. generators)
* Clean up build options using cmake_dependent_option
* Let CMake do its job in more cases, like finding the math/dl libraries and detecting and enabling LTO support
* Remove platform-specific kludges like the Fedora/flatpak LTO workaround and a bunch of Windows stuff
* Simplify Windows static builds
* Consistent formatting
