Scanner, grammar and parser changes for Switch expressions 2.0

[srikanth-sankaran]

• Restructure switch expressions grammar aligning it with JLS terminology; Eliminate unnecessary calls outs from the automaton (-> instead of ::=); fold multiple consume rules into one by parameterizing; delete dangling non-terminals (ThrowExpression ...); deduplicate unnecessary distinct non-terminals (e.g SwitchLabelExpr vs SwitchLabel ...)
• Replace the pair of tokens, first the synthetic BeginCaseExpr followed by '->' in switch rules with a single synthetic CaseArrow. The scanner will disambiguate whether a token '->' is TokenNameARROW used in lambdas or is a CaseArrow used in switch rules by checking if the automaton will shift CaseArrow or not.
• DiagnoseParser's repair of a misclassified '->' will allow it to recover perfectly! Just suppressing the message will do.
• Get rid of code engaging VanguardParser in reconnaissance missions for yield and '->' disambiguation.
• Eliminate feedback from Parser to Scanner on co-ordinates of the case statement
• Eliminate feedforward from Parser to SwitchStatement on whether it contains patterns, nulls etc; Let Switch discover it's self by itself :)
• Declutter SwitchStatement.resolve() by simplifying control flow; streamline management of secrets;
• Delete SelectionParserTest12.java as it is fully duplicated by SelectionParserTest13.java; Rename the latter to SelectionParserTest14.java and ensure it runs in the right compliance mode. Hook up this dangling junit to a parent
• Tweak a failing test case in PrimitiveInPatternsTestSH.java to work around a bug elsewhere that was masked so far. [Primitive Patterns] Wrong duplicate case error  #3265 raised as follow up.
• Adjust a few tests that result in altered diagnostics due to grammar refactoring
• Adjust test in FormatterRegressionTests.java and ResolveTests12To15.java to run at the right compliance levels