[var] various upgrades to var:

* var is promoted to the main package.
* It is no longer an opt-in thing.
* bug: var (unlike val) is allowed in old-style for loops, but if you multi-init: for (var i = 0, j="Foo";;), you now get an error that you can't do that.
* tests both for the multi-for situation and the new main package variant.

test/transform/resource/before/VarModifier.java

@@ -1,4 +1,3 @@
-//CONF: lombok.var.flagUsage = ALLOW
 import lombok.experimental.var;
 
 public class VarModifier {