JS: RegExp unknown flags support and enhanced compatibility with RegExp objects

javascript/ql/src/Security/CWE-178/CaseSensitiveMiddlewarePath.ql

@@ -65,7 +65,7 @@ predicate isCaseSensitiveMiddleware(
     arg = call.getArgument(0) and
     regexp.getAReference().flowsTo(arg) and
     exists(string flags |
-      flags = regexp.getFlags() and
+      flags = regexp.tryGetFlags() and
       not RegExp::isIgnoreCase(flags)
     )
   )

javascript/ql/test/query-tests/Security/CWE-178/CaseSensitiveMiddlewarePath.expected

@@ -6,3 +6,4 @@
 | tst.js:76:9:76:20 | /\\/baz\\/bla/ | This route uses a case-sensitive path $@, but is guarding a $@. A path such as '/BAZ/BLA' will bypass the middleware. | tst.js:76:9:76:20 | /\\/baz\\/bla/ | pattern | tst.js:77:1:79:2 | app.get ...  });\\n}) | case-insensitive path |
 | tst.js:86:9:86:30 | /\\/[Bb] ... 3\\/[a]/ | This route uses a case-sensitive path $@, but is guarding a $@. A path such as '/BAZ3/A' will bypass the middleware. | tst.js:86:9:86:30 | /\\/[Bb] ... 3\\/[a]/ | pattern | tst.js:87:1:89:2 | app.get ...  });\\n}) | case-insensitive path |
 | tst.js:91:9:91:40 | /\\/summ ... ntGame/ | This route uses a case-sensitive path $@, but is guarding a $@. A path such as '/CURRENTGAME' will bypass the middleware. | tst.js:91:9:91:40 | /\\/summ ... ntGame/ | pattern | tst.js:93:1:95:2 | app.get ... O");\\n}) | case-insensitive path |
+| tst.js:98:5:98:43 | new Reg ... Flag()) | This route uses a case-sensitive path $@, but is guarding a $@. A path such as '/BAR/1' will bypass the middleware. | tst.js:98:5:98:43 | new Reg ... Flag()) | pattern | tst.js:107:1:108:2 | app.get ... ware\\n}) | case-insensitive path |

javascript/ql/test/query-tests/Security/CWE-178/tst.js

@@ -95,7 +95,7 @@ app.get('/currentGame', function (req, res) {
 });
 
 app.get(
-    new RegExp('^/bar(.*)?', unknownFlag()), // NOT OK - Currently not flagged.
+    new RegExp('^/bar(.*)?', unknownFlag()), // NOT OK - Might be OK if the unknown flag evaluates to case insensitive one
     unknown(),
     function(req, res, next) {
         if (req.params.blah) {