Make ContentEntityTrackingManager::filterValidItemIds public

Thanks for reporting this, and sorry it even happened! By rights, we probably shouldn’t have just removed a public method, and certainly not replaced it by a protected one. So, in addition to making it public, we might also want to bring back ContentEntity::filterValidItemIds() as a reference to the new one? (Maybe deprecating it, though?)

Also, as the method continues to be independent of the class instance, it should probably still be static, as it was before? Would also make it easier for you to call it, I think. (And calling it as an instance method would still be supported, though maybe reported as code smell.)
What would you say? (Also, feedback/opinions from others very welcome.)

Attached patch would implement both of the above changes, but not 100% sure yet. (Deprecation would also need a change record, of course, if we go that route.)

(BC should not be an issue, I think, as it’s highly unlikely that anyone inherits from ContentEntityTrackingManager and overrides filterValidItemIds(). Still, it’s probably technically a BC break.)

Committed, with the deprecation. It’s pretty clear this is the clean thing to do, even though nobody seems to have noticed this for over a year (and three releases).
Thanks again for reporting this!