[mbien]

A new project type which can be used to work with arbitrary directories on your system. It integrates with project groups and other features like a regular project.

• The project is identified by a marker file or alternatively by a property stored in the NB config. User can modify this setting during project creation or afterwards using the properties window
• PR currently contains wizard, project properties window, basic actions. (todo: new-project action might be also useful or file filter settings)
• open required projects action (returns one level like the maven impl)
• potentially a building block for more features (e.g DirectoryProjectProvider with GenericProject impl and DirectoryGroup replacement #9737)
• rust modules were used as reference since they were well written and documented
• the repo was seeded with .nbgp markers for testing purposes

targets NB 33 but there is no hurry (other PRs like mvn 3.10 and jdk28 support have priority for the next release)

Assisted-by: qwen3.8-27b + granite4.2:8b