Support async parser

[fisker]

Description

Checklist

• I’ve added tests to confirm my change works.
• (If changing the API or CLI) I’ve documented the changes I’ve made (in the docs/ directory).
• (If the change is user-facing) I’ve added my changes to changelog_unreleased/*/XXXX.md file following changelog_unreleased/TEMPLATE.md.
• I’ve read the contributing guidelines.

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[fisker]

Only problem here: I can't simply make parse return a Promise, embed parser have to be sync.

Options:

1. Don't support async parser in embed format.
2. Support async printer.print() (maybe jest printer.embed() function is enough ), I was not planning to support async printer, there are some known issues in doc

Personally I prefer 1.

@kachkaev @sosukesuzuki WDYT?

[fisker]

Anyway, I'm not going to implement embed support in this PR. We can discuss in other issue #12751 .