Type discriminator is lost when serializing a Result<T> using [TranslateResultToActionResult]

When serializing a derived type as its base type, System.Text.Json will use an extra type discriminator field to communicate the actual type of the serialized data. Given a base class `Base` and a derived type `Derived`, I have observed the following behavior:

1. A controller endpoint returning `Base` will correctly include the type discriminator.
2. A controller endpoint returning `ActionResult` will include the type discriminator.
3. A controller endpoint returning `Result` will include the properties of the derived type but it will NOT include the type discriminator.

Minimal reproducible example: https://github.com/uflowie/ResultLostTypeDiscriminator

Start with the [TranslateResultToActionResult] path and compare serialization for Result with the documented Base and ActionResult cases, using the linked minimal reproducible example. Done means the Result response preserves the System.Text.Json type discriminator while retaining the derived-type properties.

Written by the indexing model from the issue text.