Clear instance based Schema Context Cache upon validation errors

Clear instance based Schema Context Cache upon validation errors

- retry yang parser exceptions one time by clearing cache
- split yangUtils into YangParserHelper (instance based) and YangUtils for non-parsering static methods
- removed public methods only used from test. Refactored to use variation with (empty) parent path
- removed use of optional for parentPath, easier to handle with just an empty string!
- make methods no longer used in production code in YangUtils are private
- udpate testware to use proper public methods instead of private methods of yang utils / parser (helper)

Issue-ID:CPS-2000

Signed-off-by: ToineSiebelink <toine.siebelink@est.tech>
Change-Id: I0c7590a5e1495d047006e7136f1bd873be37f7b0