Feature Request: use `trigEngine = ...` for `postfix`'s `match_pattern`

[sandersantema]

I'd like to use regex snippets for the match_pattern of a postfix snippet.
Such that a snippet like the following would work:

postfix({
  trig = 'pp',
  trigEngine = 'ecma',
  match_pattern = '[\\^_]?',
}, fmt('({})', { i(1) })),

[L3MON4D3]

Definitely a useful option :)
I'm tempted to say that one could just customize themselves, but since we don't really expose jsregexp, that would be a bit complicated (+ postfix does some advanced stuff, so not all that simple)

But it probably won't use the value of trigEngine, since that already determines how the trigger is handled. Maybe just passing the regex as match_ecmaregex (to also allow match_vimregex :D) uses regex instead of patterns?