Additional easy to use path for saving public data

[bkmgit]

There are architecture specific paths to the file system for internal use by an application which are set in system.c. For example on Android the following are defined:

• system-dir
• system-appdir
  Android also offers getExternalStoragePublicDirectory which was deprecated in API 29 but would seem to be helpful to have. For API 30, there is shared datasets storage though probably JNI is needed to use this.

Such a path may also be useful for downloads

If using this is problematic, then implementing some way of allowing the user to search the file system in a GUI and specify where they would like to save a file or open a file would be helpful, but seems more difficult to implement in a cross-platform manner.

[mgorges]

Correct, as per 212ab34, we now use getExternalFilesDirs as (system-directory), which is also accessible to outside tools; we also expose getFilesDir as (system-appdirectory). The change is not backwards compatible (i.e. required manual migration of files) as the previous location on /sdcard is no longer accessible to us so I know of people who disabled the patch and others who use it depending on what is more important to you - maintaining access to old files or supporting newer versions of Android. The content (system-directory) should be visible to file browsers and adb to you, though, unless we broke something recently.

Finally, sure, we can expose getExternalStoragePublicDirectory easily if that is helpful, but I currently (and in the near future) do not have the capacity to build any new JNI-based file access pieces, so you'd have to submit a pull request for an implementation.

[bkmgit]

Ok, will make a pull request.