[FIR2IR]: fix translation of this references in instance methods

Currently FirThisReceiverExpression of instance methods are translated
to references of the class' thisReceiver,
not the method's dispatch receiver,
which causes problems with IrFrameMap::typeOf,
as the class' thisReceiver is not in the typeMap.

This commit translates non-qualified "this" references of
instance methods to references of the methods' dispatch receiver.

compiler/testData/codegen/box/smartCasts/falseSmartCast.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 open class SuperFoo {
     public fun bar(): String {
         if (this is Foo) {

compiler/testData/codegen/box/smartCasts/implicitReceiver.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 open class A {
     class B : A() {
         val a = "FAIL"

compiler/testData/codegen/box/smartCasts/implicitReceiverInWhen.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 open class A {
     fun f(): String =
             when (this) {

compiler/testData/codegen/box/smartCasts/implicitToGrandSon.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 open class A {
     open fun foo() = "FAIL"
 

compiler/testData/codegen/box/smartCasts/kt19100.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 open class KFoo {
     fun foo(): String {
         if (this is KFooQux) return qux