Revert "JVM_IR: use computeIfAbsent in ClassCodegen.getOrCreate()"

This reverts commit 32518eee4b.

Reason: the commit causes lockups in ClassCodegen.

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/ClassCodegen.kt

@@ -511,7 +511,7 @@ class ClassCodegen private constructor(
                 it.origin == JvmLoweredDeclarationOrigin.CLASS_STATIC_INITIALIZER
             },
         ): ClassCodegen =
-            context.classCodegens.computeIfAbsent(irClass) { ClassCodegen(irClass, context, parentFunction) }.also {
+            context.classCodegens.getOrPut(irClass) { ClassCodegen(irClass, context, parentFunction) }.also {
                 assert(parentFunction == null || it.parentFunction == parentFunction) {
                     "inconsistent parent function for ${irClass.render()}:\n" +
                             "New: ${parentFunction!!.render()}\n" +