Fix markdownlint fixer and add markdownlint-cli2 (#5165)

* fix(tests): fix ale_c_build_dir_names being unset in tests (#5109)

- Use ale#Set() to set the ale_c_build_dir_names variable.
- Ensure SetUpLinterTest() is called before any Save commands in tests.
- Add c.vim to runtime before non-linter tests are executed.
- Remove workarounds in c.vim.

* feat: Load Prettier from cjs also

* fix: wrong command for markdownlint

* feat: explicit support for markdownlint-cli2

- Add markdownlint-cli2 linter and fixer, separate from markdownilnt-cli
- Rename markdownlint to markdownlint-cli
- Keep markdownlint as alias for markdownlint-cli

---------

Co-authored-by: w0rp <devw0rp@gmail.com>
Co-authored-by: Horacio Sanson <horacio.sanson@dena.jp>

supported-tools.md

@@ -447,7 +447,8 @@ formatting.
   * [dprint](https://dprint.dev)
   * [harper](https://github.com/elijah-potter/harper) :speech_balloon:
   * [languagetool](https://languagetool.org/) :floppy_disk: :speech_balloon:
-  * [markdownlint](https://github.com/DavidAnson/markdownlint) :floppy_disk:
+  * [markdownlint-cli](https://github.com/igorshubovych/markdownlint-cli) :floppy_disk:
+  * [markdownlint-cli2](https://github.com/DavidAnson/markdownlint-cli2) :floppy_disk:
   * [marksman](https://github.com/artempyanykh/marksman) :speech_balloon:
   * [mdformat](https://github.com/hukkin/mdformat)
   * [mdl](https://github.com/mivok/markdownlint)