Editorial: Generalize ToZeroPaddedDecimalString to support hexadecimal output

[gibson042]

No description provided.

[gibson042]

This could also use the approach of proposal-regex-escaping and replace prose with AO calls, e.g.

Suggested change

	1. If _alphabet_ is ~hex-lower~, let _S_ be the String representation of _n_, formatted as a lowercase hexadecimal number.
	1. Else if _alphabet_ is ~hex-upper~, let _S_ be the String representation of _n_, formatted as an uppercase hexadecimal number.
	1. Else, let _S_ be the String representation of _n_, formatted as a decimal number.
	1. If _alphabet_ is ~decimal~, let _S_ be BigInt::toString(ℤ(_n_), 10).
	1. Else if _alphabet_ is ~hex-lower~, let _S_ be BigInt::toString(ℤ(_n_), 16).
	1. Else, let _S_ be the ASCII-uppercase of BigInt::toString(ℤ(_n_), 16).

(importing ECMA-402's ASCII-uppercase, as is already planned for Temporal)