feat: export initialized socket client

[pmmmwh]

• 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?

No new tests are added as I believe this is a simple change and no additional functionality is added, it just exposes a bit more of the private parts.

Added a simple test for null value before init, and a "valid" client instance after init.

Motivation / Use-Case

Fixes #4261
Fixes #4324

Additional Info

I chose the simplest way to expose the initialized client, so consumers can just import the file and use it - but I'm also ok with setting it to some globals (on globalThis/window) if you think that's better (I'm unsure if mutable exports are implemented properly when compiled?).

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Michael Mok (54b2c20)

[codecov]

Codecov Report

Merging #4304 (13f2d5b) into master (4e7800e) will not change coverage.
The diff coverage is n/a.

❗ Current head 13f2d5b differs from pull request most recent head b91ae7d. Consider uploading reports for the commit b91ae7d to get more accurate results

@@           Coverage Diff           @@
##           master    #4304   +/-   ##
=======================================
  Coverage   92.18%   92.18%           
=======================================
  Files          15       15           
  Lines        1549     1549           
  Branches      591      591           
=======================================
  Hits         1428     1428           
  Misses        112      112           
  Partials        9        9           

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[snitin315]

Let's fix lint.

[pmmmwh]

I'm not sure if I should just do eslint ignore here, or should I do something more

[alexander-akait]

Just add eslint-plugin-ignore and small comment(s) why we need to it

[alexander-akait]

@pmmmwh Can we add small test cases (where we try to get client) to avoid future regressions?

[pmmmwh]

Added test!

[pmmmwh]

Completely rebased onto latest HEAD + fixed commitlint issue 😄

[alexander-akait]

Thanks

[alexander-akait]

@pmmmwh Published https://github.com/webpack/webpack-dev-server/releases/tag/v4.8.0