arrow

GH-40755: [JS] fix decimal conversions (#40729)

### Rationale for this change

Fixes  https://github.com/apache/arrow/issues/40755

Further work is required to complete:
https://github.com/apache/arrow/issues/37920

Decimals are broken - need a correct way to convert decimals to numbers
in js

Also included an option to include a denominator (BigInt(1/scale)) as
scale is part of the metadata

### What changes are included in this PR?

Submitting a correct way to convert decimals to numbers

### Are these changes tested?
Yes, includes a test

### Are there any user-facing changes?
No

 **This PR contains a "Critical Fix".**
* GitHub Issue: #37920
* GitHub Issue: #40755

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Co-authored-by: Dominik Moritz <domoritz@gmail.com>
Co-authored-by: Paul Taylor <178183+trxcllnt@users.noreply.github.com>