[mbien]

Refactors the directory-based project group action to use the new generic project type as base, combined with the pre-existing SubprojectsGroup. (see #9738 for generated design doc)

new API in lookup:

• DirectoryProjectProvider API added with GpDirectoryProjectProvider as reference impl
• Single method interface defines a single createProject(FileObject dir) method and is located in ide/projectuiapi

-> Relationship is now reversed. Functionality moved into the Lookup instead of hardcoded logic within a specialized Group impl. (could be potentially swapped out if needed)

Migration path was added to restore groups (old user config) of kind directory as generic project based SubprojectsGroup.

UI difference:

directory groups will now have their generic project displayed as node. We could probably find a way to hide it if needed.

this builds on top of #9736 and contains the commits so that it can be tested together. Commits marked with [2] belong to this PR.

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

[neilcsmith-net]

Thanks. Generally going in the right direction in my opinion. Initial comments after quick glance through -

• DirectoryProjectProvider should probably be an SPI in projectapi in https://github.com/apache/netbeans/tree/master/ide/projectapi/src/org/netbeans/spi/project The docs should be more general, and not special case groups - there are other potential use cases (at least one in the fallback PR).
• The SPI method might be better named something like findOrCreateProject to convey what it does? On the other hand, depends what the API side does ....
• General usage of the SPI should be via the project API, possibly ProjectManager::findOrCreateProject adjacent to ProjectManager::findProject ? Groups should use this via the API.
• The API should use lookup all, first wins, to support 0, 1 or multiple DirectoryProjectProvider implementations.
• Directory groups should probably not fail if no provider is available - one hiding mechanism is disabling / excluding the generic project module. The feature should not break if that is done.