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

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

@@ -1,3 +0,0 @@
-package test
-
-fun b() = "b"

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

@@ -1,5 +0,0 @@
-package test
-
-fun main(args: Array<String>) {
-    println(a() + b() + other.other())
-}