feat: implement dev server as plugin

[rishabh3112]

• This is a bugfix
• This is a feature
• This is a code refactor
• This is a test update
• This is a docs update
• This is a metadata update

For Bugs and Features; did you add new tests?

Motivation / Use-Case

The Dev Server should be implemented as a plugin for long run. This would simplify implementation of webpack serve as will give user more flexibility in multicompiler case.

The current implementation code present in DevServerPlugin.js implements few parts but still relies on Server.js to be applied.

I am currently implementing it separately at WebpackDevServerPlugin.js to simplify testing. Later on we will export only this plugin instead on Serve.js.

Breaking Changes

Yes, it would be a breaking change.

Additional Info

@alexander-akait suggested this feature. Rest, we can chat on this PR.

[codecov]

Codecov Report

Merging #3251 (84fa7f5) into master (cef3d85) will decrease coverage by 0.40%.
The diff coverage is 95.55%.

❗ Current head 84fa7f5 differs from pull request most recent head cf3da1c. Consider uploading reports for the commit cf3da1c to get more accurate results

@@            Coverage Diff             @@
##           master    #3251      +/-   ##
==========================================
- Coverage   95.72%   95.31%   -0.41%     
==========================================
  Files          33       33              
  Lines        1309     1259      -50     
  Branches      388      360      -28     
==========================================
- Hits         1253     1200      -53     
- Misses         52       55       +3     
  Partials        4        4              

Impacted Files	Coverage Δ
lib/Server.js	95.66% <95.55%> (-0.63%)	⬇️
lib/servers/WebsocketServer.js	94.11% <0.00%> (-2.95%)	⬇️
client-src/index.js	90.56% <0.00%> (-0.51%)	⬇️
lib/utils/runOpen.js	97.36% <0.00%> (-0.14%)	⬇️
client-src/utils/parseURL.js	100.00% <0.00%> (ø)
lib/utils/createDomain.js	100.00% <0.00%> (ø)
lib/utils/normalizeOptions.js	100.00% <0.00%> (+1.61%)	⬆️
client-src/utils/createSocketURL.js	100.00% <0.00%> (+3.57%)	⬆️

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[alexander-akait]

Logic should be in apply function here https://github.com/webpack/webpack-dev-server/blob/master/lib/Server.js, no need to duplicate this, all method already exists in server

[rishabh3112]

Logic should be in apply function here https://github.com/webpack/webpack-dev-server/blob/master/lib/Server.js, no need to duplicate this, all method already exists in server

Okay, I will make changes inplace then. I thought of doing it seperately to avoid breaking changes in release.

[rishabh3112]

Status

Waiting merge of #3273
WIP

[rishabh3112]

@alexander-akait what should I do next in this PR? I am done on my end 😅

[alexander-akait]

Can we avoid a lot of change, maybe better create a new PR

[rishabh3112]

Can we avoid a lot of change, maybe better create a new PR

Yup, will create a new PR for this now.