Unify script file extensions to "kts" so that IDEA, compiler and tests agree when to parse as SCRIPT.

Include kt* files into formatter test generation, to test scripting formatting

compiler/testData/cli/jvm/printArguments.args

@@ -1,3 +1,3 @@
 -printArgs
 -script
-$TESTDATA_DIR$/hello.ktscript
+$TESTDATA_DIR$/hello.kts

compiler/testData/cli/jvm/printArguments.out

@@ -1,3 +1,3 @@
-INFO: Invoking compiler org.jetbrains.jet.cli.jvm.K2JVMCompiler with arguments -printArgs -script compiler/testData/cli/jvm/hello.ktscript
+INFO: Invoking compiler org.jetbrains.jet.cli.jvm.K2JVMCompiler with arguments -printArgs -script compiler/testData/cli/jvm/hello.kts
 hello
 OK

compiler/testData/cli/jvm/script.args

@@ -1,4 +1,4 @@
 -script
-$TESTDATA_DIR$/script.ktscript
+$TESTDATA_DIR$/script.kts
 hi
 there