Introduce FirInitializerTypeMismatchChecker

compiler/testData/diagnostics/tests/smartCasts/inference/intersectionTypes.fir.kt

@@ -31,7 +31,7 @@ fun test(a: A, b: B, c: C) {
         val k = three(a, b, c)
         checkSubtype<A>(k)
         checkSubtype<B>(<!ARGUMENT_TYPE_MISMATCH!>k<!>)
-        val l: Int = three(a, b, c)
+        val l: Int = <!INITIALIZER_TYPE_MISMATCH!>three(a, b, c)<!>
 
         use(d, e, f, g, h, k, l)
     }

compiler/testData/diagnostics/tests/smartCasts/safecalls/anotherVal.fir.kt

@@ -3,6 +3,6 @@
 fun calc(x: List<String>?, y: Int?): Int {
     x?.get(y!! - 1) 
     // y!! above should not provide smart cast here
-    val yy: Int = y
+    val yy: Int = <!INITIALIZER_TYPE_MISMATCH!>y<!>
     return  yy + (x?.size ?: 0)
 }