[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/after-ecj/VarComplex.java

@@ -1,4 +1,4 @@
-import lombok.experimental.var;
+import lombok.var;
 public class VarComplex {
   private String field = "";
   private static final int CONSTANT = 20;