[Switch Expressions] Code review driven iterative clean up of Switch Expressions support

[srikanth-sankaran]

What it does

• Get rid of SwitchExpression.resolveAll and the kludge introduced by https://bugs.eclipse.org/bugs/show_bug.cgi?id=542560
• Withdraw the error A switch expression should have a non-empty switch block as it is subsumed by A switch expression should have at least one result expression
• Delete obsolete diagnostic property strings from messages.properties leaving corresponding IProblem constants deprecated
• Remove dead code in the Scanner
• Revert earlier ill thought out renaming of YieldStatement.switchExpression that actually reduces readability
• Remove misplaced attempt to diagnose about expression in place of statement from SwitchStatement.analyseCode - this is already diagnosed in SwitchExpression.resolveType()
• SwitchExpression.java: Eliminate unnecessary null checks; Opt for clearer variable names; Withdraw AST traversal method that is identical to super implementation.