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

jps-plugin/testData/incremental/pureKotlin/accessingPropertiesViaField/b.kt.new

@@ -1,3 +0,0 @@
-package test
-
-var b = "b"

jps-plugin/testData/incremental/pureKotlin/accessingPropertiesViaField/usage.kt.new

@@ -1,8 +0,0 @@
-package test
-
-fun main(args: Array<String>) {
-    val x = a + b + other.other
-    a = "aa"
-    b = "bb"
-    other.other = "other.other"
-}