Support struct FromBody parameters in minimal actions

[halter73]

This makes taking a struct as a "[FromBody]" parameter work rather than throw an exception like System.InvalidOperationException: The binary operator Equal is not defined for the types 'Contact' and 'System.Object'. Ex.

var app = WebApplication.Create(args);

app.MapPost("/api/contact", (Contact dto) => $"{dto.pcfCode} {dto.email}");

app.Run();

record struct Contact(string pcfCode, string email);

Fixes #34842

[davidfowl]

The PR description leaves much to be desired. I can't really tell where the fix is but I believe it works 😄

[halter73]

This is a fix. We don't cast from object to the struct type before checking bodyValue == null.