Respect `trigEngine`.

[L3MON4D3]

Hi! There were some additions to luasnip, some time ago actually, where lua-pattern-triggers may now be defined via trigEngine. I think it would make sense to handle snippets where it is set to "pattern" like those where regTrig is set, the other predefined ones could (with lots of effort) be handled similarly, but I don't think that's really worth it. For this to work, luasnip needs some so cmp_luasnip can tell whether a snippet has a lua-pattern as its trigger (because trigEngine is just some function, and I don't think it should be exposed) I can implement this, but pretty busy right now, so will take some time.

[saadparwaiz1]

Hiya - I'll have a look over the weekend :)