* Remove function-calc-no-invalid

* Remove calc parser

* Remove ignoring of calc parser

This change is a part of the next major version (v14).

- Remove Node 10 from CI
- Update `engines.node`

In addition, this removes needless `CI: true` (just a refactoring).
See <https://github.blog/changelog/2020-04-15-github-actions-sets-the-ci-environment-variable-to-true/>

We will no longer need the polyfill on the next major release (v14).

* Add lang to code blocks in Markdown

This change aims to make documents more readable and avoid syntax errors
by adding a language specifier to code blocks in Markdown.

To perform this task efficiently, I use two remark plugins:
- [remark-lint-code-block-syntax](https://github.com/ybiquitous/remark-lint-code-block-syntax)
- [remark-lint-fenced-code-flag](https://github.com/remarkjs/remark-lint/tree/main/packages/remark-lint-fenced-code-flag)

```diff
--- a/package.json
+++ b/package.json
@@ -66,7 +66,9 @@
   },
   "remarkConfig": {
     "plugins": [
-      "@stylelint/remark-preset"
+      "@stylelint/remark-preset",
+      "remark-lint-code-block-syntax",
+      "remark-lint-fenced-code-flag"
     ]
   },
   "jest": {
@@ -189,6 +191,8 @@
     "postcss-import": "^12.0.1",
     "prettier": "^2.2.1",
     "remark-cli": "^9.0.0",
+    "remark-lint-code-block-syntax": "^0.2.1",
+    "remark-lint-fenced-code-flag": "^2.0.1",
     "typescript": "^4.2.4"
   },
   "engines": {
```

Note: I do not recommend the addition of the plugins because they produce false positives.

* Remove deprecated files

* Remove deprecated files again

* Refactor `lib/__tests__/standalone-cache.test.js`

- Reduce redundant callbacks via `async/await` syntax. (#4881)
- Use `fs.existsSync()` instead of `fs.access()`.
  See <https://nodejs.org/api/fs.html#fs_fs_existssync_path>
- Fix the disabled test. (#5309)
- Inline redundant local variables.
- Make expectations using `typeof` more accurate.

* Reduce local variables by improving `getConfig()`