Fix copying of non-abstract functions of interfaces in JS BE

Fix copying of non-abstract functions of interfaces to implementing
classes when implementing class inherits interface via 2+ paths.

See KT-18187

compiler/testData/codegen/box/traits/kt3500.kt

@@ -1,6 +1,3 @@
-// TODO: muted automatically, investigate should it be ran for JS or not
-// IGNORE_BACKEND: JS
-
 interface BK {
     fun foo(): String = 10.toString()
 }