Don’t believe there is a definitive answer to your question.
links you to the abstract of a review article, which finds that significant (treatment requiring) yew (taxine) poisoning appears to be rare – a conclusion shared by The Swedish Poisons Information Centre.
A [i]non[/i]-referenced statement in Wikipedia gives 50 grams of the needles as a possible lethal dose.
While taxine (the most relevant toxin in yew) is not soluble in water, it will dissolve in lipids, of which mineral oil is one. Others are the oils often used in salads. I don’t know what amount of taxine that can be ingested from a salad. What I do know is that small children have a tendency to chew on a lot of things; and chewing on a yew spoon probably can result in a relevant ingestion.
Yew contains a lot of extractives, so perhaps not burn it.