openapi3filter.RegisterBodyDecoder() / openapi3filter.UnregisterBodyDecoder() based on singleton

[wtask]

The subject is ugly mostly for tests. If one test needs custom decoder, but another expects to use original one this case is sucks.

As a protection, you can offer a function to obtain a registered decoder so that it can be restored ...

[fenollp]

Could you show in code what you are suggesting please?

[wtask]

Something like

originalDecoder := openapi3filter.GetBodyDecoder({contentType})
openapi3filter.RegisterBodyDecoder({contentType}, {customDecoder})
...
openapi3filter.RegisterBodyDecoder({contentType}, originalDecoder)

Or offer default decoder registry, which will be used to fill in used decoders

openapi3filter.RegisterBodyDecoder({contentType}, openapi3filter.DefaultBodyDecoder({contentType}))