FIR checker: expose API to check if two types are compatible

This is useful for quickfixes offering casts. We don't want to offer
user to cast incompatible types.

Also, explicitly allow compare to `Nothing` and handle `Nothing` from intersection

analysis/analysis-api/testData/components/hasCommonSubtype/collections.kt

@@ -0,0 +1,9 @@
+fun test() {
+    typesHaveCommonSubtype(listOf(1), listOf(1))
+    typesHaveCommonSubtype(listOf(1), setOf(1))
+    typesHaveCommonSubtype(listOf(1), mutableSetOf(1))
+
+    typesHaveNoCommonSubtype(listOf(1), listOf(""))
+    typesHaveNoCommonSubtype(listOf(1), setOf(""))
+    typesHaveNoCommonSubtype(listOf(1), mutableSetOf(""))
+}

analysis/analysis-api/testData/components/hasCommonSubtype/dataClasses.kt

@@ -0,0 +1,14 @@
+interface I
+data class Foo(val i: Int) : I
+data class Bar(val s: String)
+
+fun test(f1: Foo, f2: Foo, f3: Foo?, b1: Bar, b2: Bar?, i: I) {
+    typesHaveCommonSubtype(f1, f2)
+    typesHaveCommonSubtype(f1, f3)
+    typesHaveCommonSubtype(f3, b2)
+    typesHaveCommonSubtype(f1, i)
+
+    typesHaveNoCommonSubtype(f1, b1)
+    typesHaveNoCommonSubtype(f1, b2)
+    typesHaveNoCommonSubtype(b1, i)
+}

analysis/analysis-api/testData/components/hasCommonSubtype/enums.kt

@@ -0,0 +1,15 @@
+enum class A {
+    A1, A2
+}
+
+enum class B {
+    B1, B2
+}
+
+fun test(a1: A, a2: A, b: B) {
+    typesHaveCommonSubtype(a1, a2)
+    typesHaveCommonSubtype(a1, A.A1)
+
+    typesHaveNoCommonSubtype(a1, b)
+    typesHaveNoCommonSubtype(A.A1, b)
+}

analysis/analysis-api/testData/components/hasCommonSubtype/simple.kt

@@ -0,0 +1,10 @@
+fun test() {
+    typesHaveCommonSubtype(1, 1)
+    typesHaveCommonSubtype("", "")
+    typesHaveCommonSubtype(null, null)
+
+    typesHaveNoCommonSubtype("", null)
+    typesHaveNoCommonSubtype(1, 1L)
+    typesHaveNoCommonSubtype(1, 1.0)
+    typesHaveNoCommonSubtype(1, "")
+}