Variant of Query::get that takes an EntryRef

[Rua]

I propose adding a variant of the three Query::get functions, Query::get_from_entry or the like, that takes an EntryRef/EntryMut instead of a World and Entity. If you want to use several queries on the same entity, then it is presumably faster to get the entry once and reuse it? Depending on what you think is better, these new functions might either be added alongside the current Query::get functions, or the existing functions be modified to work this way instead.