[IR] Transfer type annotations when substituting via IR substitutor

Other type substitutors (classic, cone-based) respect the type
annotations and copy them to the resulting type for all
cases, including type parameters.

Without this change we cannot correctly match expect/actuals
when we replace actual type parameters with expect ones in case
the actual type parameter has type enhancement annotations
(e.g., `@FlexibleNullability`).

We transfer all annotations (and not conservatively copy only type
enhancement annotations), as 1) other substitutors do that 2) other
IR type substitution utilities (e.g., `IrType.substitute`) do that.
As we will attempt reimplementing all IR type substitution utilities
via IrTypeSubstitutor, it also makes sense to completely align
the behavior.

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSubstitutor.kt

@@ -38,6 +38,7 @@ abstract class BaseIrTypeSubstitutor(private val irBuiltIns: IrBuiltIns) : Abstr
             when (val typeArgument = getSubstitutionArgument(it)) {
                 is IrStarProjection -> irBuiltIns.anyNType // TODO upper bound for T
                 is IrTypeProjection -> typeArgument.type.mergeNullability(irType)
+                    .addAnnotations(irType.annotations)
             }
         }
         if (substitutedTypeParameter != null) {