Add mapping spring RequestPart annotation to micronaut Part annotation

[altro3]

Fixed #376

[altro3]

@graemerocher Don't know how to write correct mapper for org.springframework.web.multipart.MultipartFile argument. for full support @RequestPart annotation. Could anyone help?

[graemerocher]

using org.springframework.web.multipart.MultipartFile would require a custom request argument binder probably

[altro3]

@graemerocher Yeah, I understand, that a custom mapper (bender) is needed, but I do not understand how to write such a bender correctly, because I did not find such mappers for example, so I ask for help.

Once again, I want to draw your attention to the importance of this library. In my opinion, it comes in second place in importance after the core. I don't understand why you stopped developing it. If Microsoft could be used with spring, in my opinion, it would increase the popularity of the micronaut several times.

[graemerocher]

because ultimately it is just a compatibility layer but full compatibility is not really achievable

[altro3]

I agree, but now even basic compatibility doesn't work

[graemerocher]

What doesn't work specifically?

[altro3]

look to this: #521

[CLAassistant]

All committers have signed the CLA.

[altro3]

@graemerocher I looked at everything again. It is quite difficult to make the correct mapping for the MultipartFile interface because its standard implementation is hidden and has private access.

So, I think that the basic mapping (which I did in this PR) is quite enough. We can merge it

[graemerocher]

Thanks for the contribution!