[FIR] Only add non-subsumed to overridden of intersection override

If an intersection override overrides members A.x, B.x and C.x and
B <: A, then A.x is subsumed by B.x, and we don't add it to the list of
overridden members. This fixes a false-positive MANY_IMPL_MEMBER_NOT_
IMPLEMENTED where an implementation is subsumed by an abstract override.

^KT-57092 Fixed

compiler/testData/diagnostics/tests/override/FakeOverrideModality3.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 interface A {
     fun foo() {}
 }