[meson] Implement disabled state for cairo/freetype/icu 'disabled' wasn't implemented for some of the features so they were getting found even with explicit -Dfeature=disabled, this implements it. Run the following command to test this change and check whether 'disabled' was actually effective, meson build -Dglib=disabled -Dgobject=disabled -Dcairo=disabled -Dfontconfig=disabled -Dicu=disabled -Dfreetype=disabled -Dintrospection=disabled -Dgtk_doc=disabled This is useful when one wants to integrate harfbuzz into another project via meson's subproject mechanism.