CI: drop Node.js 16

[azu]

close #1336

Changes

• Remove Node.js 16 support
• Add Node.js 18/20 to CI
• Change to use import instead of loader
  • loader cause ERR_UNKNOWN_FILE_EXTENSION error
• Use .js instead of .ts in some dynamic importing test
  • e.g. --rules-dir test need to import js file, but --import can not transpile it.

[azu]

(node:2315) ExperimentalWarning: `--experimental-loader` may be removed in the future; instead use `register()`:
--import 'data:text/javascript,import { register } from "node:module"; import { pathToFileURL } from "node:url"; register("ts-node/esm", pathToFileURL("./"));'
(Use `node --trace-warnings ...` to show where the warning was created)
(node:2315) Warning: To load an ES module, set "type": "module" in the package.json or use the .mjs extension.

/home/runner/work/textlint/textlint/packages/@textlint/feature-flag/test/textlint-feature-flag-test.ts:2
import assert from "assert";
^^^^^^

This is caused by ts-node issue.

• ERR_UNKNOWN_FILE_EXTENSION since Node.js 18.19.0 (works fine with 18.18.2) TypeStrong/ts-node#2094
• ERR_UNKNOWN_FILE_EXTENSION on Node v20.0.0 TypeStrong/ts-node#1997

[azu]

18.19.0 and 20.x change --import behavior.
It breaks tests.

We need to find a solution to this problem.

• use tsimp - some behavior is different with ts-node?

[azu]

mocha --import ts-node/esm does not handle import("./file.ts").