fix(webpack): return proper webpack plugin from useLegacyNxPlugin function

[jaysoo]

The current useLegacyNxPlugin has two issues:

1. It doesn't pass the configuration object, but rather the compiler instance.
2. It doesn't handle async correctly

This PR resolves both issues.

Current Behavior

Legacy plugins don't actually work.

Expected Behavior

Legacy plugins work.

Related Issue(s)

Fixes #

[vercel]

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1 Skipped Deployment

Name	Status	Preview	Updated (UTC)
nx-dev	⬜️ Ignored (Inspect)	Visit Preview	Aug 8, 2024 2:41pm

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• nx affected --targets=lint,test,build,e2e,e2e-ci --base=76268b7230816e938e7109f1728d3385a4b59e0a --head=a5db28deecb153064c36b0ead5b68d7f87b95206 --parallel=3
• nx run-many -t check-imports check-commit check-lock-files check-codeowners documentation --parallel=1 --no-dte
• nx-cloud record -- nx format:check --base=76268b7230816e938e7109f1728d3385a4b59e0a --head=a5db28deecb153064c36b0ead5b68d7f87b95206
• nx documentation --no-dte

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[github-actions]

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