Support empty JSP documents, or documents only containing comments

[evie-lau]

What's changed?

• Adding some JSP tests that fail to parse.

  • These are failing tests. No fix included yet in first commit - may need help with implementation.

• Attempted fix in b1c952c, included regenerating with gradle :rewrite-xml:generateAntlrSources

document
-    :   UTF_ENCODING_BOM? prolog element
+    :   UTF_ENCODING_BOM? prolog element?
    ;

[timtebeek]

Thanks a lot for the immediate fix here @evie-lau ! Great to see these covered. Should go out into a new release this Wednesday.