LibManual: Allow overriding a Node's path calculation

This is necessary for subclassing SectionNode, but generally allows more
code to rely on path() virtual dispatch always finding the correct path
regardless of the static type.

Userland/Libraries/LibManual/Node.h

@@ -25,6 +25,7 @@ public:
     virtual ErrorOr<String> name() const = 0;
     virtual bool is_page() const { return false; }
     virtual bool is_open() const { return false; }
+    virtual ErrorOr<String> path() const = 0;
 
     // Backend for the command-line argument format that Help and man accept. Handles:
     // [/path/to/documentation.md] (no second argument)

Userland/Libraries/LibManual/PageNode.h

@@ -28,7 +28,7 @@ public:
     virtual ErrorOr<String> name() const override { return m_page; };
     virtual bool is_page() const override { return true; }
 
-    ErrorOr<String> path() const;
+    virtual ErrorOr<String> path() const override;
 
     static ErrorOr<NonnullRefPtr<PageNode>> help_index_page();
 

Userland/Libraries/LibManual/SectionNode.h

@@ -32,7 +32,7 @@ public:
     virtual Node const* parent() const override { return nullptr; }
     virtual ErrorOr<String> name() const override;
     String const& section_name() const { return m_section; }
-    ErrorOr<String> path() const;
+    virtual ErrorOr<String> path() const override;
 
     virtual bool is_open() const override { return m_open; }
     void set_open(bool open);
@@ -40,6 +40,7 @@ public:
     static ErrorOr<NonnullRefPtr<SectionNode>> try_create_from_number(StringView section_number);
 
 protected:
+    // In this class, the section is a number, but in lower sections it might be the same as the name.
     String m_section;
     String m_name;