New Lint rule: check node paths

[Shinigami92]

I'm not sure if there is a CLI tool yet for that, but I would like to check that my project does not miss any path or has an incorrect path in use.

So I would like to prevent:

1. having a node path like @onready var timer: Timer = $Timer, but then $Timer does not exists
   this would need to check the .tscn file 🤔
2. even further, check if the file really exists in the system
   so when I have a res://assets/my_asset.png, but there is not my_asset.png, show an error

I accidentally missed to check in a file e.g. here:

• https://github.com/Shinigami92/ore-seeker/pull/12/files#diff-5e9f36cc843c59459f7dba39fa931ce58d38a76ad834f286f793f7ec13b2ae9bR4

and then fixed it with an additional commit:

• Shinigami92/ore-seeker@e0fb4d3

[Scony]

That would require some high-level linter that would take the entire project as input.
I've been thinking about it already. Anyway, that's the future.