Added support to use pkg shlib-{provides,requires} objects.

This effectively checks that all pkgs in a transaction to be installed
or updated, have not unmatched shared libraries, which might happen with
pkgs that had major soname bumps.

This implementation slow downs xbps_transaction_prepare() 2x, due to
the use of xbps_pkgdb_get_pkg_metadata(). A new pkgdb format is required
that adds the pkg shlib-provides objects to pkgdb, avoiding the need
to use xbps_pkgdb_get_pkg_metadata().

include/xbps_api_impl.h

@@ -191,6 +191,12 @@ xbps_dictionary_t HIDDEN xbps_find_virtualpkg_in_dict(struct xbps_handle *,
  */
 void HIDDEN xbps_transaction_revdeps(struct xbps_handle *);
 
+/**
+ * @privuate
+ * From lib/transaction_shlibs.c
+ */
+bool HIDDEN xbps_transaction_shlibs(struct xbps_handle *);
+
 /**
  * @private
  * From lib/transaction_sortdeps.c