[JS] Proposal for numeric vector `from` functions

[Brian Hulette <bh...@apache.org>]

I think the current behavior of `from` functions on IntVector and
FloatVector can be quite confusing for new arrow users. The current
behavior can be summarized as:
- if the argument is any type of TypedArray (including one of a mismatched
type), create a new vector backed by that array's buffer.
- otherwise, treat it as an iterable of numbers, and convert them as needed
- ... unless we're making an Int64Vector, then treat each input as a 32-bit
number and pack pairs together

This can give users very unexpected results. For example, you might expect
arrow.Int32Vector.from(Float32Array.from([1.0,2.0,3.0])) to yield a vector
with the values [1,2,3] - but it doesn't, it gives you the integers that
result from re-interpreting that buffer of floating point numbers as
integers.

I put together a notebook with some more examples of this confusing
behavior, compared to TypedArray.from:
https://observablehq.com/d/6aa80e43b5a97361

I'd like to propose that we re-write these from functions with the
following behavior:
- iff the argument is an ArrayBuffer or a TypedArray of the same numeric
type, create a new vector backed by that array's buffer.
- otherwise, treat is as an iterable of numbers and convert to the
appropriate type.
- no exceptions for Int64

If users really want to preserve the current behavior and use a
TypedArray's memory directly without converting, even when the types are
mismatched, they can still just access the underlying ArrayBuffer and pass
that in. So arrow.Int32Vector.from(Float32Array.from([1.0,2.0,3.0])) would
yield a vector with [1,2,3], but you could still use
arrow.Int32Vector.from(Float32Array.from([1.0,2.0,3.0]).buffer) to
replicate the current behavior.

Removing the special case for Int64 does make it a little easier to shoot
yourself in the foot by exceeding JS numbers' 53-bit precision, so maybe we
should mitigate that somehow, but I don't think combining pairs of numbers
is the right way to do that. Maybe a warning?

What do you all think? If there's consensus on this I'd like to make the
change prior to 0.14 to minimize the number of releases with the current
behavior.

Brian