Generate location() accessor for Node enum (#76)

Adds `location()` accessor to the `Node` enum, delegating to
each variant's `location()` method.

A previous commit added `location()` to individual node types 
but missed the enum itself. This allows getting the location of the 
entire node definition when working with the `Node` enum directly.

Author: alexcrocha

rust/ruby-rbs/build.rs

@@ -529,6 +529,20 @@ fn generate(config: &Config) -> Result<(), Box<dyn Error>> {
     )?;
     writeln!(file, "        }}")?;
     writeln!(file, "    }}")?;
+    writeln!(file)?;
+    writeln!(file, "    /// Returns the location of the entire node.")?;
+    writeln!(file, "    #[must_use]")?;
+    writeln!(file, "    pub fn location(&self) -> RBSLocation {{")?;
+    writeln!(file, "        match self {{")?;
+    for node in &config.nodes {
+        writeln!(
+            file,
+            "            Node::{}(node) => node.location(),",
+            node.variant_name()
+        )?;
+    }
+    writeln!(file, "        }}")?;
+    writeln!(file, "    }}")?;
     writeln!(file, "}}")?;
     writeln!(file)?;