feat(builtin): support vscode snippet variable CURRENT_TIMEZONE_OFFSET

[yuanji-dev]

CURRENT_TIMEZONE_OFFSET was added since April 2023 (version 1.78) in vscode.

Also Snippets in Visual Studio Code the doc here mentions:

CURRENT_TIMEZONE_OFFSET The current UTC time zone offset as +HH:MM or -HH:MM (example -07:00).

This PR is to support the variable in LuaSnip.

[L3MON4D3]

Hey, thanks for the contribution!
Could you exchange os.data("%z") with the more portable version described here? Seems like windows doesn't support "%z" :/

[L3MON4D3]

I think it'd be best to put that function into a new file, util/time.lua. But util/util.lua would also be fine

[yuanji-dev]

Hi @L3MON4D3
Thanks for your review, I tried to update the code based on your feedback, could you please take a look again?

[L3MON4D3]

Ah yes!
Looks perfect, thank you very much!