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/classCapturesFunction.kts

@@ -0,0 +1,14 @@
+// IGNORE_BACKEND: JS, JS_IR, JS_IR_ES6, NATIVE, WASM
+
+// expected: rv: 42
+
+val x = 6
+val y = 7
+
+fun foo() = x
+
+class A {
+    fun bar() = foo() * y
+}
+
+val rv = A().bar()