8205393: Add SourceVersion.RELEASE_13
8205394: Add source 13 and target 13 to javac
8205645: Bump maximum recognized class file version to 57 for JDK 13
8214825: Update preview language features for start of JDK 13
Reviewed-by: erikj, alanb, mchung, mcimadamore, dholmes, smarks, jjg
8207405: Compiler Tree API support for Switch Expressions (Preview)
Support for switch expression, switch with rules and multiple constants for cases.
Reviewed-by: jjg, mcimadamore, vromero
