External Libraries: Update Moment.js to 2.26.0.

Changelog: https://github.com/moment/moment/compare/2.22.2...2.26.0

This commit also fixes a deprecation warning regarding the usage of `moment.locale()` to set locale properties.

As of Moment.js 2.12.0, `moment.locale()` is deprecated and `moment.updateLocale()` should be used instead.

Additionally, minimize `moment.js` as part of build process to remove the source map reference.

This avoids a `sourceMappingURL` being in the minified file, as we don't ship source maps.

Props yoancutillas, SergeyBiryukov.
Fixes #50408.
Built from https://develop.svn.wordpress.org/trunk@48075


git-svn-id: https://core.svn.wordpress.org/trunk@47842 1a063a9b-81f0-0310-95a4-ce76da25c4cd