HTTPCORE-770: Add plusAsBlank parameter to URIBuilder for dynamic configuration

[arturobernalg]

This PR introduces a new plusAsBlank flag to the URIBuilder class, allowing users to dynamically configure whether the '+' character in query parameters should be interpreted as a space (' ') or remain as a plus ('+').

[garydgregory]

I'm not sure about creating a special case for a single character. Maybe registering a Map would be more flexible. I'm not sure what should be allowed to be mapped though.

[arturobernalg]

I'm not sure about creating a special case for a single character. Maybe registering a Map would be more flexible. I'm not sure what should be allowed to be mapped though.

HI @garydgregory
As far as I understand, according to RFC3986, spaces in URIs should be encoded as %20, and the + character is not treated as a space. Introducing a map would add unnecessary complexity since only + is treated this way in form encoding. Now, on second thought, it may be incorrect to allow users to change the plusAsBlank value. I'm not sure anymore.

[ok2c]

Now, on second thought, it may be incorrect to allow users to change the plusAsBlank value. I'm not sure anymore.

@arturobernalg This behavior is non-conformant but it is wide-spread and very common. This is a case where we ought to be lenient.

1. There is no need to have a special constructor for this flag. Just a setter should suffice.
2. Please add @since 5.4