feat: add parse zone plugin

[LucaColonnello]

Closes https://github.com/iamkun/dayjs/issues/651

I'm opening this PR based on the discussion in the linked issue above. This is something that affects many people as timezone is a complicated topic.

Example scenarios are:

• use the date timezone in format, rather than converting to the local one
• do calculations in the provided format, rather than converting to the local one
• display date and times with the original location in travel websites, rather than the user location (it confuses customers)

Example usage:

import dayjs from "dayjs";
import parseZone from "dayjs/plugins/parseZone";

dayjs.extend(parseZone);

const parsedDate = dayjs.parseZone("2016-12-21T07:01:21-08:00");

expect(parsedDate.format("MMMM D, YYYY, h:mm A")).toBe("December 21, 2016, 7:01 AM");

[LucaColonnello]

@iamkun let me know if you need me to do anything else, or add docs, I'm happy to progress this quickly. Feel free to suggest more tests if you think anything here has not been accounted for.

Having this plugin as part of dayjs, I think we would be able to catch problems and benefit from the work people can put in OSS, rather than copying and pasting this code everywhere like the issue seem to imply...

[abdirahmanjama]

@iamkun

[LucaColonnello]

I think we're just going to publish this internally to use as we need it, but I'll leave the PR open hoping eventually it will get merge or reviewed :)

[Va1]

@vronifuchsberger @abdirahmanjama guys, any ETA on when these changes will be released? it's a big pain :(

[vronifuchsberger]

not a maintainer, so unfortunately can't help you getting this in - we ended up publishing it internally in our company and re-use it in our repos until this (hopefully) get's merged 😄