Fix false warning about useless cast in property and property accessor

Note that there are some other problems, for example:
`val a = if (true) 1 as Number else 2`, here we'll get useless cast

 #KT-9551 Fixed
 #KT-9645 Fixed

compiler/testData/diagnostics/tests/cast/AsInPropertyAndPropertyAccessor.kt

@@ -0,0 +1,17 @@
+// !DIAGNOSTICS: -UNUSED_VARIABLE
+
+fun test() {
+    val a = 1 as Any?
+    val b: Number = 1 <!USELESS_CAST!>as Number<!>
+    val c = null as String?
+    val d: Number = 1 <!USELESS_CAST!>as Int<!>
+}
+
+val c1 get() = 1 as Number
+val c2: Number get() = 1 <!USELESS_CAST!>as Number<!>
+
+val d: Number
+    get() {
+        1 <!USELESS_CAST!>as Number<!>
+        return 1 <!USELESS_CAST!>as Number<!>
+    }