Detect inferred local variable types in AST

The implementation of local variable type inference adds the inferred type to the AST: http://hg.openjdk.java.net/jdk10/master/rev/48ec75306997#l8.23

As discussed in JDK-8024098, it would be nice for the AST to more closely model the source code, including whether a particular local variable's type was explicit in source or inferred from a use of var; ideally pretty-printing a variable declaration would preserve whether or not the source used var.