feat: implement plugin execution order

[fangbinwei]

• test
• doc

If there is nothing wrong with the code and design, I can try to add documentation

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Underlying tools
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

By default, the plugins are executed in the same order as before I believe

Other information:

related to #5106, #6251

Design

interface

interface Plugin {
  (): any
  after?: string|Array<string>
}

Example

vue-cli-plugin-foo/generator/index.js

module.exports = api => {
  api.render('./template')
}

vue-cli-plugin-bar/generator/index.js

module.exports = api => {
  api.render('./template')
}
module.exports.after = 'vue-cli-plugin-bar'

the 'after' can be used to fine-tune the execution order

Implement

Topological Sort Algorithm sorts the plugins by 'after'. see leetcode 210

[haoqunjiang]

I like this idea! after will be very useful.

But I'm not so sure about stage. To actually use it we need to export quite a lot of stage constants and then the internal workflow of Vue CLI becomes somehow public. I'm not sure it's maintainable.

[fangbinwei]

stage is just to ensure that the generator of @vue/cli-service is invoked firstly, and it's a substitution of sortObject. Even without 'stage', 'after' can work with the current code. Or we can just mention 'after' in the documentation?

[haoqunjiang]

Yeah, I think it can be kept as an implementation detail until we figure out a better way to use it.

In the current state, I feel it's like z-index in CSS, and z-index is very hard to manage unless there's a design system to put some constraint on it…

[haoqunjiang]

The implementation looks great to me.
Let's ship it first and add documentation in another PR later.

[leookun]

hey，wonderful realization！
But I can't seem to put some plugin ahead of built-in:commands/serve, built-in:commands/serve is the first