SparseArray/SparseVector.compact should be split into 2-3 functions

Currently, SparseArray/SparseVector.compact does two separate things which are usually not intended to be done together. It should be split into three functions:

1: Add a def filter(predicate: T => Boolean): Unit function that allows specifying a predicate which is then used to strip certain values from the array/vector without reallocation.

2: Add a function called def tailor(): Unit that cuts down the memory usage to whatever is required to hold the values.

3: For backwards compatibility, replace the function compact with a function that calls filter(x => x == zero.zero) and then tailor().