FIR: Refine operations over OriginalProjectionTypeAttribute

It's necessary because during substitution it might be necessary to combine
attributes from the original type (this) and substitution
where OriginalProjectionTypeAttribute is actually expected to be null.

Probably, it's worth considering some kind of assertion
that `other` is always null or their projections are the same.

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirUpperBoundViolatedHelpers.kt

@@ -129,17 +129,9 @@ private class FE10LikeConeSubstitutor(
 }
 
 private class OriginalProjectionTypeAttribute(val data: ConeTypeProjection) : ConeAttribute<OriginalProjectionTypeAttribute>() {
-    override fun union(other: OriginalProjectionTypeAttribute?): OriginalProjectionTypeAttribute? {
-        return other
-    }
-
-    override fun intersect(other: OriginalProjectionTypeAttribute?): OriginalProjectionTypeAttribute? {
-        return other
-    }
-
-    override fun add(other: OriginalProjectionTypeAttribute?): OriginalProjectionTypeAttribute? {
-        return other
-    }
+    override fun union(other: OriginalProjectionTypeAttribute?): OriginalProjectionTypeAttribute = other ?: this
+    override fun intersect(other: OriginalProjectionTypeAttribute?): OriginalProjectionTypeAttribute = other ?: this
+    override fun add(other: OriginalProjectionTypeAttribute?): OriginalProjectionTypeAttribute = other ?: this
 
     override fun isSubtypeOf(other: OriginalProjectionTypeAttribute?): Boolean {
         return true