Fix regression in region detection

[lionel-]

Finishes addressing posit-dev/positron#8059 (see #842 for first part).

I mistakenly thought that VSCode regions were spec'd as:

*comment_opener* #region

I.e. you need // #region in Javascript or C. However I now see that for Python, which shares with R the # symbol as comment opener, it's actually:

*comment_opener*[optional_space]region

See https://github.com/microsoft/vscode/blob/d6d5034ff685d6aab2c1f226fef288455caa7a14/extensions/python/language-configuration.json#L45-L48

So I've just copied over their regexes for detection of regions.

[juliasilge]

This is working again:

This is related to the work I did in posit-dev/positron#4174. Should we now remove this language config from the R extension:

https://github.com/posit-dev/positron/blob/4fe4b95d19119356474217c5520fbf0cf22afef5/extensions/positron-r/language-configuration/r-language-configuration.json#L29-L34

I am thinking yes. Maybe make that change when you bump ark for this PR, and then ping me for review again to confirm everything is as expected.