Sequence extension with `sorted(by:)` function should be internal

[qizh]

https://github.com/algolia/instantsearch-ios/blob/09c9fa3c762064b005fb4bb56b9f28b426b77b62/Sources/InstantSearchCore/Extensions/Sequence%2BConvenience.swift#L10-L11

So it won't pollute code suggestions for projects using this library. Also many libraries or projects have similar function implemented, usually with the same definition.

In some cases it can even produce a warning in Xcode 14. When function with the same name is used in inlinable code when InstantSearchCore is added to the project but is not imported in this specific file.

[qizh]

Still the case in Xcode 15