lib: add binary package internalization step

- internalize scripts so we can use them before unpacking packages.
- moves some required metadata checks out of the package unpack stage
  so errors do not leave the system in a half unpacked state.

xbps_transaction_files will be changed later to use the loaded
files.plist instead of opening each binary package on its own again.

lib/transaction_commit.c

@@ -110,6 +110,15 @@ xbps_transaction_commit(struct xbps_handle *xhp)
 	 */
 	xbps_fetch_unset_cache_connection();
 
+	/*
+	 * Internalize metadata of downloaded binary packages.
+	 */
+	if ((rv = xbps_transaction_internalize(xhp, iter)) < 0) {
+		xbps_dbg_printf(xhp, "[trans] failed to internalize transaction binpkgs: "
+		    "%s\n", strerror(-rv));
+		goto out;
+	}
+
 	/*
 	 * Collect files in the transaction and find some issues
 	 * like multiple packages installing the same file.