Simplify MockHttpServletRequestBuilders hierarchy

[snicoll]

In Spring Framework 6.2.x we introduced a hierarchy for MockHttpServletRequestBuilder and MockMultipartHttpServletRequestBuilder to add support for AssertJ. Unfortunately, this broke source and binary compatibility.

This has been restored in #33229 but we should take the opportunity of a major release to simplify the code.

This task is mostly about reverting 265299c

[Lublanski]

Hi @snicoll , I’d like to take a look at this issue.

Can i start to working on this?

[snicoll]

@Lublanski thanks but given that's about a revert, I think it's better if the team handles it.

[Lublanski]

@snicoll Thanks for the reply. Oh, okay, I've been a developer for 5 years and I'm looking to start contributing to the Spring ecosystem. I'm looking for my first issue.

I'll look for other issues without any assignees to try to make my first contribution.

Sincerely, Vinciius Lublanski

[snicoll]

No, thank you! Without your comment I think I would have overlooked this one.