[fixes #2849] Make ToString's onlyExplicitlyIncluded a config key.

test/transform/resource/before/ToStringExplicitIncludeConf.java

@@ -0,0 +1,7 @@
+//CONF: lombok.toString.onlyExplicitlyIncluded = true
+
+@lombok.ToString
+class ToStringExplicitIncludeConf {
+	int x;
+	@lombok.ToString.Include int y;
+}