languages: Fix RTL language file generation

The 'rtl' flags for Arabic and Hebrew was inadvertantly deleted
in 7ff3c94e1 (over a year ago, in November 2020!) but it's actually been
broken since the introduction of 'updatelang', in 2305966d (July 2020)

The fix here is to change the 'RTL' flag from an <options> section in
the language file to a comment in the header.  It's not as pure in a
design sense but it makes for a much cleaner implementation.

I may further revamp this by making the 'RTL' flag into an explicit
LANG_xxx string

Change-Id: I48f394adfadc0aa804fd67690c87cc28f04fccdc

apps/lang/arabic.lang

@@ -14,6 +14,8 @@
 # This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 # KIND, either express or implied.
 #
+# LANGUAGE_IS_RTL
+#
 # Arabic language file, translated by:
 # - Mohamed Tarek
 # - Raafat Akkad

apps/lang/hebrew.lang

@@ -14,6 +14,8 @@
 # This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 # KIND, either express or implied.
 #
+# LANGUAGE_IS_RTL
+#
 # Hebrew language file, translated by:
 # - Ariel Saghiv
 # - Liberman Shachar