Digits in PartitionNotationSubPattern's "scientificExponent" partition should be replaced by the numbering system's digits

[trflynn89]

Referring to: https://tc39.es/ecma402/#sec-partitionnotationsubpattern

Steps 1 and 2 of the "number" case are to replace the digits in the number n with the digits of the specified numbering system.

These steps should likely also be applied to the exponent digits in the "scientificExponent" case.

V8 and SpiderMonkey behave this way already, for example:

> Intl.NumberFormat('ar', {notation: 'scientific'}).format(100000)
"١اس٥"

However, an implementation that doesn't replace the exponent digits (such as the @formatjs/intl-numberformat polyfill) would instead yield:

> Intl.NumberFormat('ar', {notation: 'scientific'}).format(100000)
"١اس5"