[Docs] Misleading description of paramsSerializer

[denexapp]

Hi,

fetchBaseQuery accepts an optional paramsSerializer.

This docs page says that the params will be passed to URLSearchParams directly:

params will be given directly to new URLSearchParams()

But if we look at the code, in fact there's a default transformation happening - an internal stripUndefined function is applied.

This transformation doesn't apply if a custom paramsSerializer is provided.

This can lead to an unexpected behavior. If user provides a basic custom paramsSerializer that takes the params and passes them to a new URLSearchParams, its behavior is gonna be different from the default paramsSerializer, contrary to what the docs say.

The description of paramsSerializer should be updated to mention this behavior

[markerikson]

Could you file a docs PR to update that description? Thanks!