LibFileSystem: Add FileSystem::is_regular_file

Author: https://github.com/shannonbooth
Commit: b2d33c5689
Pull-request: https://github.com/SerenityOS/serenity/pull/19844
Reviewed-by: https://github.com/AtkinsSJ ✅

Userland/Libraries/LibFileSystem/FileSystem.h

@@ -25,6 +25,9 @@ ErrorOr<String> real_path(StringView path);
 bool exists(StringView path);
 bool exists(int fd);
 
+bool is_regular_file(StringView path);
+bool is_regular_file(int fd);
+
 bool is_directory(StringView path);
 bool is_directory(int fd);