FIR body resolve: support subject type calculation

compiler/fir/resolve/testData/loadCompiledKotlin/coroutines/Basic.txt

@@ -1,4 +1,4 @@
-public final fun builder(c: R|error: createSuspendFunctionType not supported|): R|kotlin/Unit|
+public final fun builder(c: R|class error: createSuspendFunctionType not supported|): R|kotlin/Unit|
 
 public final class Controller : R|kotlin/Any| {
     public final suspend fun suspendFun(): R|kotlin/Unit|

compiler/fir/resolve/testData/loadCompiledKotlin/type/SuspendFunction.txt

@@ -1,7 +1,8 @@
-public final fun test1(): R|error: createSuspendFunctionType not supported|
+public final fun test1(): R|class error: createSuspendFunctionType not supported|
 
-public final fun test2(): R|error: createSuspendFunctionType not supported|
+public final fun test2(): R|class error: createSuspendFunctionType not supported|
 
-public final fun test3(): R|kotlin/collections/List<error: createSuspendFunctionType not supported>|
+public final fun test3(): R|kotlin/collections/List<class error: createSuspendFunctionType not supported>|
+
+public final fun test4(): R|class error: createSuspendFunctionType not supported|
 
-public final fun test4(): R|error: createSuspendFunctionType not supported|

compiler/fir/resolve/testData/resolve/expresssions/when.kt

@@ -1 +1,6 @@
-fun foo() = if (true) 1 else 0
+fun foo() = if (true) 1 else 0
+
+fun bar(arg: Any?) = when (arg) {
+    is Int -> arg as Int
+    else -> 42
+}

compiler/fir/resolve/testData/resolve/expresssions/when.txt

@@ -10,3 +10,14 @@ FILE: when.kt
         }
 
     }
+    public final fun bar(arg: R|kotlin/Any|?): R|kotlin/Int| {
+        ^bar when (R|<local>/arg|) {
+            ($subj$ is R|kotlin/Int|) ->  {
+                (R|<local>/arg| as R|kotlin/Int|)
+            }
+            else ->  {
+                Int(42)
+            }
+        }
+
+    }