[FIR2IR] Don't generate excess IR block from FirSingleExpressionBlock

This is needed to unify K1 and K2 behavior.

#KT-65064
#KT-63781 Fixed

compiler/testData/ir/irText/expressions/ifWithArrayOperation.kt

@@ -0,0 +1,29 @@
+fun topLevelMethod() {
+    val array = intArrayOf(1)
+
+    if(true) { array[0] = 2 } else { array[0] = 3 }
+    if(true)   array[0] = 4   else   array[0] = 5
+
+    if(true) { array[0] += 6 } else { array[0] += 7 }
+    if(true)   array[0] += 8   else   array[0] += 9
+
+    when(array[0]) {
+        1 -> { array[0] = 10 }
+        else -> { array[0] = 11 }
+    }
+
+    when(array[0]) {
+        1 -> array[0] = 12
+        else -> array[0] = 13
+    }
+
+    when(array[0]) {
+        1 -> { array[0] += 14 }
+        else -> { array[0] += 15 }
+    }
+
+    when(array[0]) {
+        1 -> array[0] += 16
+        else -> array[0] += 17
+    }
+}