Handle flow comments with leading spaces (#9168)

* check for spaces and tabs before a flow comment

* fix issue with using string index and shift interchangably

* update tests

* Use update charcodes version

* Disallow flow-comments in flow-comments and check for unterminated comments

scripts/tests/flow/run_babel_parser_flow_tests.js

@@ -98,7 +98,7 @@ function update_whitelist(summary) {
       );
     });
 
-  const newLines = disallowed
+  const newLines = summary.disallowed.failure
     .map(({ test }) => test.file)
     .filter(test => oldLines.indexOf(test) === -1);