meson: ecpg: Split definition of static and shared libraries

meson: ecpg: Split definition of static and shared libraries

Required for correct resource file generation, as the resource files should
only be added to the shared library.

This also fixes a bunch of issues in the .pc files.

Previously I tried to avoid building sources twice, once for the static and
once for the shared libraries. We could still do so, but it's not clear that
it's worth the complication.

Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Discussion: https://postgr.es/m/20220927011951.j3h4o7n6bhf7dwau@awork3.anarazel.de