gplugin/gplugin

Add a doc alias target and bump the meson requirement to 0.52.0

Testing Done:
Ran locally

Reviewed at https://reviews.imfreedom.org/r/582/
debian/tmp/usr/include/gplugin-1.0/gplugin
debian/tmp/usr/include/gplugin-1.0/gplugin.h
debian/tmp/usr/include/gplugin-1.0/gplugin-native.h
debian/tmp/usr/lib/*/libgplugin.so
debian/tmp/usr/lib/*/pkgconfig/gplugin.pc
debian/tmp/usr/share/gir-1.0/GPlugin-1.0.gir
debian/tmp/usr/share/gplugin/valgrind/gplugin.supp
debian/tmp/usr/share/vala/vapi/gplugin.deps
debian/tmp/usr/share/vala/vapi/gplugin.vapi