Previously pkg-config files generated by the pkgconfig modules for static libraries
with dependencies could only be used in a dependencies with `static: true`.
This was caused by the dependencies only appearing in Libs.private even
if they are needed in the default linking mode. But a user of a
dependency should not have to know if the default linking mode is static
or dynamic; A dependency('somelib') call should always pull in all
needed pieces into the build.
Now for meson build static libraries passed via `libraries` to the generate
method automatically promote dependencies to public.
Currently only not found deps implicitly pulled from a Library object
are ignored. We should also ignore not found deps passed directly to
generate() method.
This makes the unit testing more complicated because libfoo pkgconfig
dependency cannot be found when generated from the within the same
meson.build.