[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/smartcasts/controlStructures/earlyReturnInNonExhaustiveWhen.fir.txt

@@ -0,0 +1,16 @@
+FILE: earlyReturnInNonExhaustiveWhen.kt
+    public final fun foo(str: R|kotlin/String?|): R|kotlin/Int| {
+        when () {
+            ==(R|<local>/str|, Null(null)) ->  {
+                ^foo Int(-1)
+            }
+        }
+
+        when () {
+            ==(R|<local>/str|.R|kotlin/String.length|, Int(123)) ->  {
+                ^foo Int(123)
+            }
+        }
+
+        ^foo Int(321)
+    }

compiler/fir/analysis-tests/testData/resolve/smartcasts/controlStructures/earlyReturnInNonExhaustiveWhen.kt

@@ -0,0 +1,10 @@
+// ISSUE: KT-24901
+
+fun foo(str: String?): Int {
+    when {
+        str == null -> return -1
+    }
+    if (str.length == 123)
+        return 123
+    return 321
+}

compiler/fir/analysis-tests/testData/resolve/smartcasts/controlStructures/returnFromWhen.fir.txt

@@ -0,0 +1,19 @@
+FILE: returnFromWhen.kt
+    public final fun test_1(name: R|kotlin/String?|): R|kotlin/Unit| {
+        when (R|<local>/name|) {
+            ==($subj$, Null(null)) ->  {
+                ^test_1 Unit
+            }
+        }
+
+        R|<local>/name|.R|kotlin/String.length|
+    }
+    public final fun test_2(name: R|kotlin/String?|): R|kotlin/Unit| {
+        when (lval s: R|kotlin/String?| = R|<local>/name|) {
+            ==($subj$, Null(null)) ->  {
+                ^test_2 Unit
+            }
+        }
+
+        R|<local>/name|.R|kotlin/String.length|
+    }

compiler/fir/analysis-tests/testData/resolve/smartcasts/controlStructures/returnFromWhen.kt

@@ -0,0 +1,15 @@
+// ISSUE: KT-52262
+
+fun test_1(name: String?) {
+    when (name) {
+        null -> return
+    }
+    name.length
+}
+
+fun test_2(name: String?) {
+    when (val s = name) {
+        null -> return
+    }
+    name.length
+}