feat: replace eslint-loader by eslint-webpack-plugin

[fangbinwei]

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

Other information:
close #5926, using eslint-webpack-plugin can fix the problem of eslint-loader caused by cache-loader, related issue: #3065, #5399, #4425

eslint@7 contains a break change related to plugin resolution

In previous versions, ESLint resolved all plugins from the current working directory by default. Starting in ESLint v7.0.0, plugins are resolved relative to the directory path of the entry configuration file.

After checking the rfc, I believe new behavior is reasonable and it does not conflict with the current project. So I didn't set resolvePluginsRelativeTo like create-react-app

TODO

• bump version of eslint-webpack-plugin after this important pr of eslint-webpack-plugin is merged
• eslint-webpack-plugin option threads(default true now) may cause performance problem, related issue. maybe set threads to false.
• cacheIdentifier

[fangbinwei]

• It seems some test failed because there isn't enough memory in the container.
  set 'threads' of eslint-webpack-plugin by 'options.parallel' to solve this problem.

[fangbinwei]

After bumping the version of eslint-webpack-plugin, the tests failed. It seems threads is not compatible with webpack mutil-compiler(build commonjs2 umd lib, etc) create a new issue webpack-contrib/eslint-webpack-plugin#56
Also considering the threads related issue, maybe it's best to threads false now.

[haoqunjiang]

Looks good!

[ap-patel]

Hi @sodatea @fangbinwei , this fix doesn't seem to be in the latest release for vue-cli-eslint (4.5.15) which was released 3 months ago.
Current release points to

https://github.com/vuejs/vue-cli/blob/22a8a788e84cacec0c07407214f87a0819399ebf/packages/%40vue/cli-plugin-eslint/index.js

If i want this fix, is it safe to use 5.0.0-rc2?

[haoqunjiang]

Yes, I think so.