[JVM_IR, IR] Remove more needless temporary variables.

Avoid using a separate origin for temporary variables introduced
for for loops. That doesn't add anything and gives one more case
for optimizations to deal with.

Extend the JVM specific optimizations to remove temporary
variables to deal with more cases encountered in for loops
lowering.

compiler/testData/codegen/bytecodeText/forLoop/forInStringSpecialized.kt

@@ -9,5 +9,5 @@ fun test() {
 // 0 hasNext
 // 0 nextChar
 // 0 INVOKEINTERFACE
-// 1 ISTORE 4
-// 1 ILOAD 4
+// 1 charAt \(I\)C
+// 1 length \(\)I