AK: Add dirname() to FileSystemPath

AK/FileSystemPath.cpp

@@ -45,10 +45,19 @@ void FileSystemPath::canonicalize()
         }
     }
     if (canonical_parts.is_empty()) {
-        m_string = m_basename = "/";
+        m_string = m_basename = m_dirname = "/";
         return;
     }
 
+    StringBuilder dirname_builder(approximate_canonical_length);
+    for (int i = 0; i < canonical_parts.size() - 1; ++i) {
+        auto& canonical_part = canonical_parts[i];
+        if (is_absolute_path || i != 0)
+            dirname_builder.append('/');
+        dirname_builder.append(canonical_part);
+    }
+    m_dirname = dirname_builder.to_string();
+
     m_basename = canonical_parts.last();
     auto name_parts = m_basename.split('.');
     m_title = name_parts[0];

AK/FileSystemPath.h

@@ -12,6 +12,7 @@ public:
     bool is_valid() const { return m_is_valid; }
     const String& string() const { return m_string; }
 
+    const String& dirname() const { return m_dirname; }
     const String& basename() const { return m_basename; }
     const String& title() const { return m_title; }
     const String& extension() const { return m_extension; }
@@ -25,6 +26,7 @@ private:
 
     Vector<String> m_parts;
     String m_string;
+    String m_dirname;
     String m_basename;
     String m_title;
     String m_extension;