typing: fix uses of MNullableType in AForExpr

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
typing: set mpropdef.has_supercall = true for all init calls

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
nitj: introduce nitj a compiler from nit to java

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>