Refactor format function and add createMomentDate function

[nathanss]

What?

Creates a function createMomentDate that allows creating a moment object by passing a date string and a PHP-style format that gets converted using the formatMap object.

Why?

In the PR woocommerce/woocommerce#46932 implemented this outside of the @wordpress/date library to deal with a bug in Chinese date formats.

How?

It uses the existing formatMap object and creates a new function to create the moment object from the date and the PHP-style date format.

Testing Instructions

No manual tests needed, it has unit tests.

Testing Instructions for Keyboard

Screenshots or screencast

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