[3.x] Fix import hints breaking node paths in animations

[rburing]

Backport #43044. Since I originally made that PR before 3.x and master diverged in this area this was easy for me to do.

[rburing]

Just to clarify: this PR adds exactly the same code as in the master version #43044, up to minor syntax changes (comparison to an empty String and iteration over a List now both using the old syntax). Indeed, this can be observed by scrolling through both diffs. The only real difference is where the code is added, namely in _fix_node (which is the only possible place in 3.x), whereas it was _pre_fix_node in master. The same test cases from #38809 and #38163 can be used to test the bugfix (open the project, observe the animation not working, reimport the model, observe the animation working).

[akien-mga]

Thanks!