pnp-webpack-plugin cannot work outside of pnp runtime.

[missing1984]

Context

Trying to add yarn pnp support to cypress and ran into following error

**Details:** Error: Cannot find module 'pnpapi'
Require stack:
- /Users/mluo/Library/Caches/Cypress/6.6.1/Cypress.app/Contents/Resources/app/packages/server/node_modules/pnp-webpack-plugin/index.js
- /Users/mluo/Library/Caches/Cypress/6.6.1/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-batteries-included-preprocessor/index.js
- /Users/mluo/Library/Caches/Cypress/6.6.1/Cypress.app/Contents/Resources/app/packages/server/lib/plugins/child/run_plugins.js
- /Users/mluo/Library/Caches/Cypress/6.6.1/Cypress.app/Contents/Resources/app/packages/server/lib/plugins/child/index.js
Require stack:
- /Users/mluo/Library/Caches/Cypress/6.6.1/Cypress.app/Contents/Resources/app/packages/server/node_modules/pnp-webpack-plugin/index.js
- /Users/mluo/Library/Caches/Cypress/6.6.1/Cypress.app/Contents/Resources/app/packages/server/node_modules/@cypress/webpack-batteries-included-preprocessor/index.js
- /Users/mluo/Library/Caches/Cypress/6.6.1/Cypress.app/Contents/Resources/app/packages/server/lib/plugins/child/run_plugins.js
- /Users/mluo/Library/Caches/Cypress/6.6.1/Cypress.app/Contents/Resources/app/packages/server/lib/plugins/child/index.js
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:972:15)
    at Function.external_module_.Module._resolveFilename (/Users/mluo/workspace/gitlab/ui-platform/projects/apps/px/.pnp.js:38306:54)
    at Module._load (internal/modules/cjs/loader.js:848:27)
    at external_module_.Module._load (/Users/mluo/workspace/gitlab/ui-platform/projects/apps/px/.pnp.js:38162:36)
    at Function.f._load (electron/js2c/asar_bundle.js:5:12738)
    at Module.require (internal/modules/cjs/loader.js:1032:19)
    at require (internal/modules/cjs/helpers.js:72:18)
    at getSourceLocation (/Users/mluo/Library/Caches/Cypress/6.6.1/Cypress.app/Contents/Resources/app/packages/server/node_modules/pnp-webpack-plugin/index.js:39:15)
    at makeResolver (/Users/mluo/Library/Caches/Cypress/6.6.1/Cypress.app/Contents/Resources/app/packages/server/node_modules/pnp-webpack-plugin/index.js:53:26)
    at Object.<anonymous> (/Users/mluo/Library/Caches/Cypress/6.6.1/Cypress.app/Contents/Resources/app/packages/server/node_modules/pnp-webpack-plugin/index.js:147:10)
    at Module._compile (internal/modules/cjs/loader.js:1152:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1173:10)
    at Module.load (internal/modules/cjs/loader.js:992:32)
    at Module._load (internal/modules/cjs/loader.js:885:14)
    at external_module_.Module._load (/Users/mluo/workspace/gitlab/ui-platform/projects/apps/px/.pnp.js:38162:36)
    at Function.f._load (electron/js2c/asar_bundle.js:5:12738)

Cypress server (an Electron app)is forking a new process to compile plugins from user project, however, the webpack config and compile code live with Cypress app.

After chatting with merceyz in channel, it looks like pnp-webpack-plugin assumes it been located within the pnp project and it's not the case here.

https://discord.com/channels/226791405589233664/654372321225605128/822584013377241108

Would that be possible to port what we've done in webpack 5/enhanced-resolve so pnp-webpack-plugin can work in that scenario.