The Haxe extension adds a "Haxe Dependencies" tree view to the explorer. It contains all Haxelibs and classpaths from the currently selected Configuration, as well as the Haxe Standard Library. Classpaths that are part of the current workspace are ignored to avoid duplicating what the regular File Explorer already displays.
The ability to browse through the files of a Haxelib is particularly useful for Haxelib authors or contributors.
Note: if you want to navigate to a particular type in a dependency, using Workspace Symbols is usually quicker / more convenient.
Just like the regular explorer view, "Haxe Dependencies" also supports the
"explorer.autoReveal" setting (enabled by default). So whenever you open a file of a dependency (via workspace symbols, drag-and-dropping the file into VSCode...), the view automatically reveals and selects that file.