New range tag for local dates with syntax like:
```
[date-range from=2022-01-06T13:00 to=2022-01-08 timezone=Australia/Sydney]
```
Previously, 2 dates in one line were considered as range. It was hard to decide if 2 dates are range when they were in separate lines or have some content between them.
New explicit tag should clearly distinguish between single date and range.
Common code from `addLocalDate` is extracted to `addSingleLocalDate`.
Both `addLocalDate` and new `addLocalRange` are using `addSingleLocalDate`.
Also, `defaultDateConfig` was extracted to have one place for all possible parameters.
- prefers insertAdjacentHTML over innerHTML as it's much faster in this case (about 5x)
- memoizes tz.guess()
- memoizes list of timezones
- inlines template
- applies main element class in one pass
All in all for a very edge case of about 80 dates it should be faster of about 15/20ms.
You might wonder why this matters. It turns out in some locales like
French, we replace quotation marks with « and » -- this should likely
not happen before BBCode is parsed but that is not the case for this
plugin. The plugin has code to handle this situation, but it means extra
spaces are inserted around the time zone which breaks it.
This fix allows us to supply extra whitespace and will show the correct
time zone.
