Add some options to Project Settings to silence warnings in AnimationMixer caching

[TokageItLab]

• Closes Animation cache errors immediately after deleting node #85316

This PR is a salvaged version of #69480 with corrected error handling for finding path as pointed out in #85368. Also, as discussed several times in the past, invalid paths will be changed to a warning instead of an error since it is not a critical.

However, since cases where animations do not play due to path mismatches may occur to a certain extent in beginners, so the default is true; There are cases where the destination of add_child scenes is wrong, the name of the Skeleton is changed due to the use of retargeting and etc. It means, flag have been inverted from the original PR (#69480).

And finally, I added a statement in the warning that it is possible to turn off that warning in project settings.

• Supersedes/closes Add option throw_error_with_invalid_path to Project Setting and remove cache error from AnimationTree #69480
• Supersedes/closes Removing redundant errors during animation mixer cache update #85368
• Fixes AnimationTree spamming error when switching scene #83418 (maybe)

[KoBeWi]

Even if you disable the warning, the AnimationPlayer will spam errors:

It should be using get_node_or_null() to avoid that.

[TokageItLab]

Even if you disable the warning, the AnimationPlayer will spam errors:

@KoBeWi Can you send an MRP? I assume the error is the problem somewhere else where the setting not affected (maybe AnimationTrackEditor?).

[KoBeWi]

Spam is probably exaggerated, there is just a single error print when clicking the AnimationPlayer.

Bug.tscn.txt

[TokageItLab]

@KoBeWi The null checks in AnimationTrackEditor were missing in some places, so I fixed them. Errors have gone.

The KeyType determination in ValueTrack fails when the node cannot be found with path, but I assume it seems to be expected behavior.

[TokageItLab]

Oops, sorry I accidentally closed it while cleaning up an old branch.

[TokageItLab]

Changed some lines to adopt #88247.

[akien-mga]

Thanks!