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/psi/script/ComplexScript.txt

@@ -1,4 +1,4 @@
-JetFile: ComplexScript.ktscript
+JetFile: ComplexScript.kts
   PACKAGE_DIRECTIVE
     <empty list>
   SCRIPT

compiler/testData/psi/script/Import.txt

@@ -1,4 +1,4 @@
-JetFile: Import.ktscript
+JetFile: Import.kts
   PACKAGE_DIRECTIVE
     <empty list>
   SCRIPT

compiler/testData/psi/script/Shebang.txt

@@ -1,4 +1,4 @@
-JetFile: Shebang.ktscript
+JetFile: Shebang.kts
   PsiComment(SHEBANG_COMMENT)('#!/usr/bin/env kotlin')
   PsiWhiteSpace('\n\n')
   PACKAGE_DIRECTIVE

compiler/testData/psi/script/ShebangIncorrect.txt

@@ -1,4 +1,4 @@
-JetFile: ShebangIncorrect.ktscript
+JetFile: ShebangIncorrect.kts
   PACKAGE_DIRECTIVE
     <empty list>
   SCRIPT

compiler/testData/psi/script/SimpleScript.txt

@@ -1,4 +1,4 @@
-JetFile: SimpleScript.ktscript
+JetFile: SimpleScript.kts
   PACKAGE_DIRECTIVE
     <empty list>
   SCRIPT