TISTUD-6683 Gracefully handle invalid XML attribute values

- be able to handle unquoted attribute values that begin with digits in our scanner
- mark unquoted attribute values as parse errors and recover in our parser
- mark attributes with no value as parse errors and recover in our parser

With the new changes, since the parser is gracefully handling all the parser errors, we might be having the list of all errors after the parsing. I would like to see if the parser can report 2 errors when there are 2 unquoted attribute values - something on the similar lines
String source = "<note attr=123></note><note attr1=321></note>";