Warn on unknown command line arguments

This eases troubleshooting when working with command line arguments.

Warnings are only printed if the argument does not exist as a file
or directory path (relative or absolute). This allows positional arguments
to keep working as they are now, without printing warnings when a project
reads positional arguments to perform operations on files (e.g. when
drag-and-dropping a file onto a project executable).

This now prints a warning:

    godot --non-existent-argument

This still doesn't print a warning, as it's an user argument:

    godot -- --non-existent-argument

This doesn't print a warning if the file/folder path exists:

    godot /path/to/file.txt

A warning is still printed if the file/folder doesn't exist. Drag-and-drop
associations always refer to existing files/folders, so that scenario was
unlikely to be encountered.

0 files changed, 0 insertions, 0 deletions