xbps_transaction_*: multiple performance improvements (v2).

This commit implements multiple performance improvements
to the transaction code:

- Don't process xbps_pkg_name() N times each time we access
  its package dictionary (via pkgdb or rpool), just do it once
  at xbps_pkgdb_init() time. At pkgdb init time, it just creates
  a property in pkgdb, "pkgname". At rpool time, each time a
  package is accessed, the "pkgname" string property is added.

- The package transaction dictionary contains the "transaction"
  object to know what's the pkg type. This has been changed to an
  uint8, this simplifies the logic and it's faster than checking
  a string object. See xbps_trans_type_t and xbps_transaction_pkg_type().

- Fixed the issue that was marked with XXX in transaction shlibs
  checking code. This has been fixed and improved and resources are
  now just freed as expected.

- Simplified random code all over the place, avoiding unnecessary
  allocations or operations.

- Rename some transaction files to have a better description.

This is my first rototill to the code in 2020.

bin/xbps-install/state_cb.c

@@ -66,7 +66,7 @@ state_cb(const struct xbps_state_cb_data *xscd, void *cbdata UNUSED)
 		printf("[*] pkgdb upgrade in progress, please wait...\n");
 		break;
 	case XBPS_STATE_REPOSYNC:
-		printf("[*] Updating `%s' ...\n", xscd->arg);
+		printf("[*] Updating repository `%s' ...\n", xscd->arg);
 		break;
 	case XBPS_STATE_TRANS_ADDPKG:
 		if (xscd->xhp->flags & XBPS_FLAG_VERBOSE)