[FIR] Implement checker for exhaustive when's in expression position

compiler/testData/diagnostics/tests/when/withSubjectVariable/nestedWhenWithSubject.fir.kt

@@ -38,4 +38,4 @@ fun test4() {
                 2 -> bar(x, y)
             }
     }
-}
+}

compiler/testData/diagnostics/tests/when/withSubjectVariable/smartcastToEnum.fir.kt

@@ -1,18 +0,0 @@
-// !LANGUAGE: +VariableDeclarationInWhenSubject
-// !DIAGNOSTICS: -UNUSED_VARIABLE
-
-enum class E { FIRST, SECOND }
-
-fun testSmartcastToEnumInSubjectInitializer1(e: E?) {
-    val x1 = when (val ne = e!!) {
-        E.FIRST -> "f"
-        E.SECOND -> "s"
-    }
-}
-
-fun testSmartcastToEnumInSubjectInitializer2(e: E?) {
-    val x2 = when (val ne: Any = e!!) { // NB explicit type annotation
-        E.FIRST -> "f"
-        E.SECOND -> "s"
-    }
-}

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

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !LANGUAGE: +VariableDeclarationInWhenSubject
 // !DIAGNOSTICS: -UNUSED_VARIABLE
 

compiler/testData/diagnostics/tests/when/withSubjectVariable/smartcastToSealed.fir.kt

@@ -1,20 +0,0 @@
-// !LANGUAGE: +VariableDeclarationInWhenSubject
-// !DIAGNOSTICS: -UNUSED_VARIABLE
-
-sealed class Either
-class Left : Either()
-class Right : Either()
-
-fun testSmartcastToSealedInSubjectInitializer1(x: Any?) {
-    val y1 = when (val either = x as Either) {
-        is Left -> "L"
-        is Right -> "R"
-    }
-}
-
-fun testSmartcastToSealedInSubjectInitializer2(x: Any?) {
-    val y2 = when (val either: Any = x as Either) { // NB explicit type annotation
-        is Left -> "L"
-        is Right -> "R"
-    }
-}

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

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !LANGUAGE: +VariableDeclarationInWhenSubject
 // !DIAGNOSTICS: -UNUSED_VARIABLE