Use require.resolve to find CSS modules in node_modules

[penx]

Further to #70693 which was reworked by @aeschli in 8f72934 due to issues with require.resolve and webpack.

Fixes #78894
Fixes microsoft/vscode-css-languageservice#136

The current implementation of resolving the path to a CSS module in node_modules has significant limitations.

Using require.resolve directly should be the most solid approach but can't be used in code that is webpacked.

This PR allows us to use require.resolve via a module proxy (requireresolveproxy) and marking the module as a commonjs external in the webpack config.

Potential alternative approaches:

• implement as per https://github.com/microsoft/TypeScript/blob/master/src/compiler/moduleNameResolver.ts (ideally by importing it directly and with support from someone who wrote this)
• use https://github.com/browserify/resolve
• use require.resolve in the same way as it's used here https://github.com/microsoft/vscode-languageserver-node/blob/master/server/src/resolve.ts (ideally with support/direction from someone who knows how we could replicate this in css-language-features, @dbaeumer?)

[penx]

This builds fine now when I run yarn gulp -- vscode-darwin, however I'm not sure how I run the production build on MacOS in order to test it. I have tried cd out-build && node main.js but get Error: Cannot find module 'electron'.

[penx]

Confirmed this is working in the dev build (yarn watch and ./scripts/code.sh) so taking out of draft - I can test in the production build too if someone lets me know how!

[penx]

this is using require rather than import due to not having .ts typings for requireresolveproxy - happy to resolve in another way if someone can suggest how

[penx]

Pretty sure the failing CI is unrelated to this PR

  49 passing (2s)
  1 failing

  1) Links node module resolving:

      AssertionError [ERR_ASSERTION]: 'file:///d%3A/a/1/s/extensions/css-language-features/server/test/linksTestFixtures/foo/hello.html' == 'file:///d%3A/a/1/s/extensions/css-language-features/server/test/linksTestFixtures/node_modules/foo/hello.html'
      + expected - actual

      -file:///d%3A/a/1/s/extensions/css-language-features/server/test/linksTestFixtures/foo/hello.html
      +file:///d%3A/a/1/s/extensions/css-language-features/server/test/linksTestFixtures/node_modules/foo/hello.html
      
      at assertLink (D:\a\1\s\extensions\css-language-features\server\out\test\links.test.js:23:16)
      at assertLinks (D:\a\1\s\extensions\css-language-features\server\out\test\links.test.js:37:13)

[aeschli]

That's the test that I added for the node module resolving.

[penx]

Replaced by #81555