Drop Node.js 10 support & Require Node.js >= 12

[SukkaW]

Continuing #3508 & #3698.

With Node.js 12 we will be able to use:

• Object.fromEntries
• Array#values
• String#matchAll
• Array#flat, Array#flatMap
• Well-formed JSON.stringify: https://github.com/tc39/proposal-well-formed-stringify
• Class field: https://github.com/tc39/proposal-class-fields
• Static field: https://github.com/tc39/proposal-static-class-features/

Also, worker_threads requires Node.js 12+ as well, which is important for multi-core usage proposal (#4355).

On the other hand, async/await is significantly faster than native Promise and its performance is now comparable to that of Bluebird:

Ref: https://blog.kuzzle.io/bluebird-vs-native-vs-async/await-state-of-promises-performances-in-2019
Ref: https://v8.dev/blog/fast-async

---

Eventually we will drop Node.js 10. The question is whether we should bump minimum required Node.js version to 12 before we publish Hexo 5.0.0.

cc @hexojs/core @curbengh @segayuu @seaoak @tomap @stevenjoezhang

[tomap]

So, we will drop node 12 with hexo 6?

[SukkaW]

@tomap Yeah, wait for Hexo 6.

[stevenjoezhang]

Node.js 10 will reach EOL on April 30, 2021

https://github.com/nodejs/Release

See also hexojs/hexo-generator-index#51 hexojs/hexo-generator-index#59

String.prototype.matchAll requires Node.js 12.4.0: hexojs/hexo-util#246

[stevenjoezhang]

Node.js 12 supports esm import export without --experimental-modules flag

Automated ESM conversion tools: https://github.com/lebab/lebab https://github.com/wessberg/cjstoesm
(Both of them could not perfectly handle naming conflicts of const and import)

[stevenjoezhang]

Closed by #4750