Docs: dynamically generated list of available locales page

[fturmel]

This PR converts the documentation generation code to TypeScript and adds a new dynamically generated documentation page that lists available locales as a table and as JSON. I think this will be very valuable to the community to have easy access to this information.

You can preview the generated page here: https://github.com/date-fns/date-fns/blob/9bb51691f201c3ec05ab832acbc5d478f2e5c47a/docs/i18nLocales.md

A few things to point out:

• I turned on the jsdoc-to-markdown cache, as it seems to work well and detects file changes correctly. On my machine, it takes almost 2 minutes on an empty cache to generate the docs, but completes in 420ms with cache and one source file modified.
• This new docs generation script will fail if the @summary jsdoc tags of locales are not unique. Hoping this will help people build out locale selectors without duplicate entries. I made some adjustments to a few locale's jsdoc entries to fix typos, uniqueness and precision.
• To complete the TypeScript conversion, I had to add some type definitions to package.json. I kept the changes to a minimum.

Hope you like it!

EDIT: also fixes a docs bug for FP ESM usage, see comment below

[tan75]

DIscussion:
#2724

[fturmel]

@bartduisters Apologies, as mentioned in the other thread I was going off the CLDR for the English name of the locale and found that Flemish was in there. https://unicode-org.github.io/cldr-staging/charts/40/summary/nl.html

Just pushed a commit using your recommendations.

[fturmel]

Last commit in this PR fixes dosc ESM usage examples for FP (see #2124).

Before notice //
import { formatISO } from 'date-fns/esm//fp'

After
import { formatISO } from 'date-fns/fp'

It also removes 'umd' usage since that is not supported anymore and not displayed on the docs website.

[fturmel]

soft reset to fix all the conflicts. Also removed the TypeScript and broken locale stats from output since these are not relevant anymore.

[p-fernandez]

This PR seems stale. Is there any plans to merge it anytime soon?