reporting unnamed fields in an FCS helper function

[smoothdeveloper]

first bit of proof of concept for #15665

note to self: https://github.com/dotnet/fsharp/pull/14055 for reference of fixers dealing with DU fields.

I'm not clear if there are other things that could be checked, maybe we'd like to report bindings that are deconstructing types in function signatures; but this doesn't feel like an idiom to discourage (to me).

• [x] report DU case fields
• [x] report Exception fields

[psfinaki]

Hi @smoothdeveloper, are you still interested in tackling this PR? :)

[nojaf]

This is available as an analyzer at https://ionide.io/ionide-analyzers/suggestion/004.html. I would not pursue to have this in the compiler.

[abonie]

Closing since the same functionality is already available as an analyzer