Fix bad method links in docstrings (#13471)

# Description

Seems like I developed a bit of a bad habit of trying to link

```rust
/// [`.foo()`]
```

in docstrings, and this just doesn't work automatically; you have to do 

```rust
/// [`.foo()`](Self::foo)
```

if you want it to actually link. I think I found and replaced all of
these.

# User-Facing Changes

Just docs.

crates/nu-plugin-protocol/src/evaluated_call.rs

@@ -85,19 +85,19 @@ impl EvaluatedCall {
         self
     }
 
-    /// Builder variant of [`.add_positional()`].
+    /// Builder variant of [`.add_positional()`](Self::add_positional).
     pub fn with_positional(mut self, value: Value) -> Self {
         self.add_positional(value);
         self
     }
 
-    /// Builder variant of [`.add_named()`].
+    /// Builder variant of [`.add_named()`](Self::add_named).
     pub fn with_named(mut self, name: Spanned<impl Into<String>>, value: Value) -> Self {
         self.add_named(name, value);
         self
     }
 
-    /// Builder variant of [`.add_flag()`].
+    /// Builder variant of [`.add_flag()`](Self::add_flag).
     pub fn with_flag(mut self, name: Spanned<impl Into<String>>) -> Self {
         self.add_flag(name);
         self