[FIR] Add NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY diagnostic

compiler/testData/diagnostics/tests/incompleteCode/incompleteAssignment.fir.kt

@@ -1,3 +1,5 @@
+// COMPARE_WITH_LIGHT_TREE
+
 package sum
 
 import java.util.*
@@ -6,7 +8,7 @@ fun sum(a : IntArray) : Int {
     <!UNRESOLVED_REFERENCE!>res<!> = 0
     for (e in a)
         <!UNRESOLVED_REFERENCE, VARIABLE_EXPECTED!>res<!> +=<!SYNTAX!><!>
-}
+<!NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY{LT}!>}<!>
 fun main() {
     test(0)
     test(1, 1)
@@ -27,4 +29,4 @@ fun <T: Any> assertEquals(actual : T?, expected : T?, message : Any? = null) {
         else
             throw AssertionError(message)
     }
-}
+}