feat: migrate the `codePlugin` from `@vuepress/markdown` to `plugin-prismjs`

[pengzhanbo]

Before submitting the PR, please make sure you do the following

• [x] Read the Contributing Guidelines.
• [x] Provide a description in this PR that addresses what the PR is solving. If this PR is going to solve an existing issue, please reference the issue (e.g. close #123).

What is the purpose of this pull request?

• [ ] Bug fix
• [x] New feature
• [ ] Other

Description

see https://github.com/vuepress/core/issues/1550

Screenshots

Before

After

[coveralls]

Pull Request Test Coverage Report for Build 9124434582

Details

• 84 of 89 (94.38%) changed or added relevant lines in 9 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+2.2%) to 51.909%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
plugins/plugin-prismjs/src/node/resolveHighlighter.ts	0	2	0.0%
plugins/plugin-prismjs/src/node/prismjsPlugin.ts	0	3	0.0%
<!--	Total:	84	89	94.38%	-->

Totals
Change from base Build 9123655949:	2.2%
Covered Lines:	771
Relevant Lines:	1350

---

💛 - Coveralls

[meteorlxy]

Please also migrate and try to improve the test cases. Code fence plugin is an important feature.

[pengzhanbo]

Please also migrate and try to improve the test cases. Code fence plugin is an important feature.

Added test cases identical to the codePlugin in @vuepress/core.

[pengzhanbo]

The current PR has been merged into #137, so close this PR and continue the discussion in #137.