Minor: use ".touch" extension instead of ".new" in incremental compilation tests when it possible

jps-plugin/testData/incremental/pureKotlin/simpleClassDependency/Foo.kt.new

@@ -1,8 +0,0 @@
-package test
-class Foo {
-    fun f() {
-        Bar()
-    }
-
-    class Boo
-}