[Test] Add regression tests for issues which are fixed in K2

Related issues:
KT-10879, KT-18055, KT-20617, KT-23873
KT-25668, KT-31191, KT-33108, KT-41013
KT-51827, KT-53886, KT-56624, KT-58447
KT-58458, KT-58751, KT-58814, KT-60597
KT-62806, KT-63258, KT-63444, KT-65101
KT-65408, KT-65844, KT-66186

^KT-65926 Fixed

compiler/testData/diagnostics/tests/when/withSubjectVariable/unnamedSubject.fail

@@ -0,0 +1,4 @@
+java.lang.NullPointerException
+	at org.jetbrains.kotlin.types.expressions.PatternMatchingTypingVisitor$Subject$Variable.makeValueArgument(PatternMatchingTypingVisitor.kt:149)
+	at org.jetbrains.kotlin.types.expressions.PatternMatchingTypingVisitor$checkWhenCondition$1.visitWhenConditionInRange(PatternMatchingTypingVisitor.kt:509)
+	at org.jetbrains.kotlin.psi.KtVisitorVoid.visitWhenConditionInRange(KtVisitorVoid.java:1015)

compiler/testData/diagnostics/tests/when/withSubjectVariable/unnamedSubject.kt

@@ -0,0 +1,8 @@
+// FIR_IDENTICAL
+// ISSUE: KT-58458
+
+fun box() =
+    when (val<!SYNTAX!><!> = <!UNRESOLVED_REFERENCE!>x<!>) {
+        in <!UNRESOLVED_REFERENCE!>y<!> -> ""
+        else -> ""
+    }