Fix grammar pertaining to C variadics in function pointer types

The grammar was incorrect since

* C variadics `...` no longer need to be preceded by a normal parameter
  * that's the case since <rust-lang/rust#124048>
* C variadics don't need to be the final element, `fn(..., i32)` is
  perfectly fine
* C variadics can indeed be named (e.g., `fn f(_: ...)` or `fn(v: ...)`)
* C variadics can be followed by a comma (e.g., `fn(...,)`)

Author: fmease

src/types/function-pointer.md

@@ -5,23 +5,17 @@ r[type.fn-pointer.syntax]
 ```grammar,types
 BareFunctionType ->
     ForLifetimes? FunctionTypeQualifiers `fn`
-       `(` FunctionParametersMaybeNamedVariadic? `)` BareFunctionReturnType?
+       `(` MaybeNamedFunctionParameters? `)` BareFunctionReturnType?
 
 FunctionTypeQualifiers -> Safety? (`extern` Abi?)?
 
 BareFunctionReturnType -> `->` TypeNoBounds
 
-FunctionParametersMaybeNamedVariadic ->
-    MaybeNamedFunctionParameters | MaybeNamedFunctionParametersVariadic
-
 MaybeNamedFunctionParameters ->
     MaybeNamedParam ( `,` MaybeNamedParam )* `,`?
 
 MaybeNamedParam ->
-    OuterAttribute* ( ( IDENTIFIER | `_` ) `:` )? Type
-
-MaybeNamedFunctionParametersVariadic ->
-    ( MaybeNamedParam `,` )* MaybeNamedParam `,` OuterAttribute* `...`
+    OuterAttribute* ( ( IDENTIFIER | `_` ) `:` )? ( Type | `...` )
 ```
 
 r[type.fn-pointer.intro]