Move JavaScript of LTI 1.3 login self posting form to a JS file.

Author: taniwallach

htdocs/js/LTILogin/ltilogin.js

@@ -0,0 +1 @@
+document.getElementById('ltiRepost')?.submit();

templates/ContentGenerator/LTI/self_posting_form.html.ep

@@ -1,9 +1,8 @@
+<%= javascript $c->url({ type => 'webwork', name => 'htdocs', file => 'js/LTILogin/ltilogin.js' }),
+        defer => undef =%>
 <%= form_for $form_target, method => 'POST', enctype => 'application/x-www-form-urlencoded',
 	name => 'ltiRepost', id => 'ltiRepost', begin =%>
 	% for (keys %$form_params) {
 		<%= hidden_field $_ => $form_params->{$_} =%>
 	% }
 <% end =%>
-<%= javascript begin =%>
-	document.ltiRepost.submit();
-<% end =%>