UriBuilder - Correct the treatment of Optional types.

[robinroos]

This PR is an alternative to #25925 and all the discussion on that PR remains relevant.

This PR is an improvement because:

1. it retains the existing public API without alteration, and
2. it applies a consistent treatment even when an Optional is included amongst a list of arguments (varargs).

I have taken the liberty of updating the interface documentation.

It previously stated

If no values are given, the resulting URI will contain the query parameter name only, ...

I have complimented this by stating that

If the only values given are {@code Optional} instances for which {@code isPresent()} returns {@code false} then the query parameter name will not be added.

My justification is that calling the method with an explicit null (no parameters are given) is deliberately different from calling the method with one or more instances of Optional.empty.

Furthermore, please note that the current implementation is deficient when invoked with one or more Optionals as arguments, in that the text written to the URL is the .toString() of the Optional instance and not the .toString() of the value it contains; invoke queryParam("name", Optional.of("value")) and what is added to the URL is "?name=Optional[value]", not the expected "?name=value".

Something needs to be done, and I believe this PR (which omits the queryParam entirely if all passed values are Optional.empty) is the correct solution.