Fix call enum's metadata regression (#3513)

This fixes an issue introduced in
https://github.com/paritytech/substrate/pull/14101, in which I removed
the `Call` enum's documentation and replaced it with a link to the
`Pallet` struct, but this also removed any docs related to call from the
metadata.

I tried to add a regression test for this, but it seems to me that this
is not possible, given that using `type-info` we only assert in type-ids
for `Call`, `Event` and `Error`. I removed some doc comments from a test
setup in `frame-support-test` to demonstrate the issue there. @jsdw do
you have any comments on this?

I also fixed a small issue in the custom html/css of `polkadot-sdk-doc`
crate, making sure it does not affect the rust-doc page of all other
crates.

- [x] Investigate a regression test
- [x] prdoc

substrate/frame/support/procedural/src/pallet/expand/call.rs

@@ -18,7 +18,7 @@
 use crate::{
 	pallet::{
 		expand::warnings::{weight_constant_warning, weight_witness_warning},
-		parse::call::{CallVariantDef, CallWeightDef},
+		parse::call::CallWeightDef,
 		Def,
 	},
 	COUNTER,
@@ -112,22 +112,7 @@ pub fn expand_call(def: &mut Def) -> proc_macro2::TokenStream {
 	}
 	debug_assert_eq!(fn_weight.len(), methods.len());
 
-	let map_fn_docs = if !def.dev_mode {
-		// Emit the [`Pallet::method`] documentation only for non-dev modes.
-		|method: &CallVariantDef| {
-			let reference = format!("See [`Pallet::{}`].", method.name);
-			quote!(#reference)
-		}
-	} else {
-		// For the dev-mode do not provide a documenation link as it will break the
-		// `cargo doc` if the pallet is private inside a test.
-		|method: &CallVariantDef| {
-			let reference = format!("See `Pallet::{}`.", method.name);
-			quote!(#reference)
-		}
-	};
-
-	let fn_doc = methods.iter().map(map_fn_docs).collect::<Vec<_>>();
+	let fn_doc = methods.iter().map(|method| &method.docs).collect::<Vec<_>>();
 
 	let args_name = methods
 		.iter()
@@ -309,7 +294,7 @@ pub fn expand_call(def: &mut Def) -> proc_macro2::TokenStream {
 			),
 			#(
 				#cfg_attrs
-				#[doc = #fn_doc]
+				#( #[doc = #fn_doc] )*
 				#[codec(index = #call_index)]
 				#fn_name {
 					#(