[FIR] Add regression tests for number of issues fixed in K2

List of issues:
KT-4113,  KT-6822,  KT-7389,  KT-17817, KT-20223
KT-21463, KT-24503, KT-24737, KT-24779, KT-24901
KT-27261, KT-28668, KT-30497, KT-30756, KT-36958
KT-37365, KT-37490, KT-38288, KT-41038, KT-41721
KT-42136, KT-42169, KT-42449, KT-42715, KT-43553
KT-43603, KT-43846, KT-43936, KT-46288, KT-46301
KT-47373, KT-47484, KT-47490, KT-47495, KT-47750
KT-47815, KT-47870, KT-48975, KT-49024, KT-49045
KT-50134, KT-50160, KT-50550, KT-51045, KT-51143
KT-51796, KT-52262, KT-52424, KT-52860, KT-52934
KT-53086, KT-53494, KT-53671, KT-53752, KT-53819
KT-54478, KT-54518, KT-54931, KT-54990, KT-55138
KT-55379, KT-55555, KT-56243

compiler/fir/analysis-tests/testData/resolve/samConversions/nothingVararg.fir.txt

@@ -0,0 +1,7 @@
+FILE: main.kt
+    public final fun test(x: R|A<*>|): R|kotlin/Unit| {
+        R|<local>/x|.R|SubstitutionOverride</A.call: R|kotlin/Unit|>|(vararg(call@fun <anonymous>(y: R|kotlin/Any?|): R|kotlin/Unit| <inline=Unknown>  {
+            Q|kotlin/Unit|
+        }
+        ))
+    }

compiler/fir/analysis-tests/testData/resolve/samConversions/nothingVararg.kt

@@ -0,0 +1,16 @@
+// ISSUE: KT-41721
+
+// FILE: SAM.java
+public interface SAM<T> {
+  void apply(T x);
+}
+
+// FILE: A.java
+public class A<T> {
+  public void call(SAM<T>... block) { block[0].apply(null); }
+}
+
+// FILE: main.kt
+fun test(x: A<*>) {
+    x.call({ y: Any? -> Unit })
+}