Solve this by adding find() overloads to HashTable and SinglyLinkedList
that take a templated functor for comparing the values.
This allows HashMap to call HashTable::find() without having to create
a temporary Entry for use as the table key. :^)
This is prep work for supporting HashMap with NonnullRefPtr<T> as values.
It's currently not possible because many HashTable functions require being
able to default-construct the value type.
The underlying data structure is a singly-linked list of Vector<T>.
We never shift any of the vector contents around, but we batch the memory
allocations into 1000-element segments.
Also run it across the whole tree to get everything using the One True Style.
We don't yet run this in an automated fashion as it's a little slow, but
there is a snippet to do so in makeall.sh.
