Fix missing icons on macOS

Craft adds share/icons into blacklist, which will not be copied into the bundle:

bin/Packager/applications_blacklist_macos.txt

# we are using the icon.rcc on mac
share/icons/.*

As a workaround, on macOS, set ICON_INSTALL_DIR to another path

Solve Bug 416049 - Connect icon in the top bar is invisible in dark mode on MacOS