[JS] Inconsistent behavior in Int64Builder with/without BigNum

[asfimport]

When the Int64Builder is used in a context without BigNum, appending two numbers combines them into a single Int64:

> v = Arrow.Builder.new({type: new Arrow.Int64()}).append(1).append(2).finish().toVector()
> v.get(0)
Int32Array [ 1, 2 ]

Whereas the same process with BigNum creates two new Int64s.

Reporter: Brian Hulette / @TheNeuralBit
Assignee: Brian Hulette / @TheNeuralBit

PRs and other links:

• GitHub Pull Request #4691

_{Note: This issue was originally created as ARROW-5714. Please see the migration documentation for further details.}

[asfimport]

Brian Hulette / @TheNeuralBit:
I'm pretty sure the issue is that we don't account for stride here: https://github.com/apache/arrow/blob/master/js/src/builder/buffer.ts#L108

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 4691
#4691