add cmake build support

[ITotalJustice]

almost feature parity with the makefile builds, however still have to use makepkg manually to build ext4 and ntfs-3g. i can use cmake command to do this but havent tried yet.

an example for how to use it:

cmake -B build -DCMAKE_TOOLCHAIN_FILE=${DEVKITPRO}/cmake/Switch.cmake -DUSBHSFS_GPL=ON -DUSBHSFS_EXAMPLE=ON
cmake --build build -j16

this will build the lib with ext4+ntfs and the example.

[ITotalJustice]

things left to do before merge

• [ ] release / debug builds (usbhsfsd and usbhsfs)
• [ ] document cmake build version in readme