Include the problem source hash in the problemUUID passed to PG.

If a problem is rendered using any of the source hash parameters
(`problemSource`, `rawProblemSource`, or `uriEncodedProblemSource`),
then an MD5 hex of the utf8 encoded source is added tot he problemUUID
that is passed to PG.

This means that if a problem is rendered by source and the source
changes, then dynamically generated images will be regenerated.  The PG
problem editor uses the rawProblemSource, so this means that if the code
for a problem changes in the code mirror window, then dynamic images
will be regenerated.

This replaces openwebwork#2277 and openwebwork/pg#983. This
is better as it reliably detects code changes, and it does not need a
change to PG.  Thanks @drdrew42 for pointing this out.

lib/WeBWorK/Utils/Rendering.pm

@@ -25,6 +25,8 @@ WeBWorK::Utils::Rendering - utilities for rendering problems.
 use Mojo::IOLoop;
 use Mojo::JSON qw(decode_json);
 use Data::Structure::Util qw(unbless);
+use Digest::MD5 qw(md5_hex);
+use Encode qw(encode_utf8);
 
 use WeBWorK::Utils qw(formatDateTime);
 
@@ -48,7 +50,14 @@ sub constructPGOptions ($ce, $user, $set, $problem, $psvn, $formFields, $transla
 	# If a problemUUID is provided in the form fields, then that is used.  Otherwise we create one that depends on
 	# the course, user, set, and problem.  Note that it is not a true UUID, but will be converted into one by PG.
 	$options{problemUUID} = $formFields->{problemUUID}
-		|| join('-', $user->user_id, $ce->{courseName}, 'set' . $set->set_id, 'prob' . $problem->problem_id);
+		|| join('-',
+			$user->user_id,
+			$ce->{courseName},
+			'set' . $set->set_id,
+			'prob' . $problem->problem_id,
+			defined $translationOptions->{r_source} && ${ $translationOptions->{r_source} }
+			? 'sourcehash' . md5_hex(encode_utf8(${ $translationOptions->{r_source} }))
+			: ());
 
 	$options{probNum}        = $problem->problem_id;
 	$options{questionNumber} = $options{probNum};