Implement script instance capturing in script lowering

for regular classes only. Reimplementing the main behavior of the
old BE and implementing few cases on top of it.
#KT-19423 fixed

compiler/testData/codegen/script/scriptInstanceCapturing/classCapturesExtensionIndirect2x.kts

@@ -0,0 +1,21 @@
+// IGNORE_BACKEND: JS, JS_IR, JS_IR_ES6, NATIVE, WASM
+// IGNORE_BACKEND: JVM
+
+// expected: rv: kotlin.Unit
+
+class C {
+    fun foo() {
+        B()
+    }
+}
+
+class A
+fun A.ext() = Unit
+
+class B {
+    fun bar() {
+        A().ext()
+    }
+}
+
+val rv = C().foo()