JVM_IR: Support init blocks in inline classes

Put their content to constructor-impl, so they are called during
constructor call, but they are not called during boxing, because
box-impl calls <init> and not constructor-impl.

 #KT-28055 In progress

compiler/testData/diagnostics/tests/inlineClasses/presenceOfInitializerBlockInsideInlineClass.kt

@@ -2,9 +2,9 @@
 // !DIAGNOSTICS: -UNUSED_VARIABLE
 
 inline class Foo(val x: Int) {
-    <!INLINE_CLASS_WITH_INITIALIZER!>init<!> {}
+    init {}
 
-    <!INLINE_CLASS_WITH_INITIALIZER!>init<!> {
+    init {
         val f = 1
     }
 }