Don't use double ref vars in Debug derive (#380, #289, #382)

## Synopsis

While looking into #328 I realized the current situation around Pointer
derives
and references was even weirder because we store a double-reference to
the
fields in the local variables for Debug, but not for Display. The reason
we
were doing this was because of #289.


## Solution

This stops storing a double-reference, and only adds the additional
reference
in the places where its needed.

impl/src/fmt/debug.rs

@@ -82,7 +82,7 @@ fn expand_struct(
  .ident
  .clone()
  .map_or_else(|| syn::Member::Unnamed(i.into()), syn::Member::Named);
- quote! { let #var = &&self.#member; }
+ quote! { let #var = &self.#member; }
  });
 
  let body = quote! {
@@ -275,7 +275,7 @@ impl<'a> Expansion<'a> {
  None => {
  let ident = format_ident!("_{i}");
  Ok(quote! {
- derive_more::__private::DebugTuple::field(#out, #ident)
+ derive_more::__private::DebugTuple::field(#out, &#ident)
  })
  }
  },
@@ -316,7 +316,7 @@ impl<'a> Expansion<'a> {
  )
  }),
  None => Ok(quote! {
- derive_more::core::fmt::DebugStruct::field(#out, #field_str, #field_ident)
+ derive_more::core::fmt::DebugStruct::field(#out, #field_str, &#field_ident)
  }),
  }
  })?;