Add Linux support

[kyv001]

In posix systems, cp is used instead of copy, so the command used to copy files needs to depend on OS type.
On Linux, Fontconfig is needed to be linked with the executables.
Also, the dynamic library juce-full doesn't work for whatever reason, so the static version juce-full-static is used instead.
GCC does not compile (and creates strange error messages) so only LLVM is supported.
SynthEngineDemo.vst3 needs to be installed manually because it is not copied to the right place automatically for some reason.

The vcpkg-overlay is still needed to be updated for VocalShaper to be able to compile on Linux.

[FangCunWuChang]

I will test and resolve SynthEngineDemo.vst3 copy and juce-full runtime issues on Linux in the near future.

[FangCunWuChang]

I will do these later before merging this PR:

• Test on Linux
• Fixed SynthEngineDemo.vst3 copy issue
• Fixed juce-full runtime issue

[kyv001]

Another problem is that it keeps getting segmentation faults (in ActionDispatcher.cpp ActionDispatcher::dispatch) when creating an audio bus. That makes it not usable on Linux.

[kyv001]

In ActionDispatcher::dispatch, the object action is used (action->getName()) AFTER it is released. Here I get the name before releasing it, so that it does not segfault.

[FangCunWuChang]

In ActionDispatcher::dispatch, the object action is used (action->getName()) AFTER it is released. Here I get the name before releasing it, so that it does not segfault.

I understand. Different compilers calculate function parameters in different orders.
Suggest creating a separate PR for this bug.

[kyv001]

Need to update vcpkg-overlay to use the x64-linux-llvm triplet.