FIR: handle synthetic properties with unstable smartcast

Synthetic properties from Java getter/setters need to be specially
handled so that candidates from such symbols are marked with unstable.

compiler/testData/diagnostics/tests/smartCasts/intersectionScope/unstableSmartCast.fir.kt

@@ -1,37 +0,0 @@
-// !CHECK_TYPE
-
-interface A {
-    fun foo(): CharSequence?
-    fun baz(x: Any) {}
-}
-
-interface B {
-    fun foo(): String
-    fun baz(x: Int): String =""
-    fun baz(x: Int, y: Int) {}
-
-    fun foobar(): CharSequence?
-}
-
-interface C {
-    fun foo(): String
-    fun baz(x: Int): String =""
-    fun baz(x: Int, y: Int) {}
-
-    fun foobar(): String
-}
-
-var x: A = null!!
-
-fun test() {
-    x.foo().checkType { _<CharSequence?>() }
-
-    if (x is B && x is C) {
-        x.foo().checkType { _<CharSequence?>() }
-        x.baz("")
-        x.baz(1).checkType { _<Unit>() }
-        x.baz(1, <!TOO_MANY_ARGUMENTS!>2<!>)
-
-        x.<!UNRESOLVED_REFERENCE!>foobar<!>().checkType { _<String>() }
-    }
-}