This adds a cross-platform date/time formatting library in CLJC, with
(nearly) identical output in both JVM and JS environments.

The only known difference is week numbers.

CLJS (through Moment.js) has ordinal numbers, and renders the week
number as "34th". Neither the JVM nor Clojure has a handy library for
this (I'm sure it's out there somewhere, but it seems like a silly
dep to add) so it renders week numbers as simply "34".

Both platforms have date formatters that use pattern strings (eg.
`"YYYY-MM-dd"`) to turn date/time objects into strings. There's a strong
resemblance in how these work and what letters stand for what parts of
the date and time, but they are far from identical.

Rather than try to hackily convert one set of strings to another with
regexes or other manipulations, this PR defines a set of names for
fragments of dates (eg. `:year`, `:day-of-week-full`, `:hour-24-dd`)
and includes functions to transform a list of these keys into a
platform-specific format function.

This is portable and transparent, and can be written in Clojure or
JS code:

```clj
[:year "-" :month-dd "-" :day-of-month-dd]   ; 2022-04-08
[:month-full " " :day-of-month-d ", " :year] ; April 8, 2022
[:hour-12-dd ":" :minute-dd " " :am-pm]      ; 7:52 AM
```

```js
[":year", "-", ":month-dd", "-", ":day-of-month-dd"]   ; 2022-04-08
[":month-full", " ", ":day-of-month-d", ", ", ":year"] ; April 8, 2022
[":hour-12-dd", ":", ":minute-dd", " ", ":am-pm"]      ; 7:52 AM
```

Note that the original code allowed an unrecognized `:date-style` string
to be used directly as the formatting string. With the move to
formatting data structures that no longer works. Instead there is a
fixed map of format strings to the above data structures, that contains
all the currently used `:date-style` inputs.

If some caller needs a new format someday, we can either: (a) add the
style to the map; or (b) pass the data structure form directly to the
`:date-format` option, which if provided is used as the format.

It's tempting to go to all the call sites and replace these `:date-style`
strings with the new format structures. However, the strings are still
embedded in the `:visualization_settings` in user appDBs, so we still
need to recognize them.

Most of the existing functions in the TS library have the same API.

The set of allowed `:date-style` and `:time-style` values is turned into
a type using `keyof`, so that we get precise type-checking of these
values rather than simply `string`.

One function has been dropped from the API: `getDateFormatFromStyle`.
There was no practical way to implement it using the new format data
structures. The only caller was the date format column settings, and it
has been rewritten to use the formatted string for its sample date as
its key instead.