Implement incremental resolution: Fast Refresh on new files, changed symlinks, etc.

[robhogan]

• Fast Refresh: correctly reflect when filesystem changes should result in different resolutions - eg creating a more specific platform variant, installing a more local node_modules, symlinks added or traversed symlinks deleted.
• Unblock resolution caching.

Differential Revision: D52391695

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This pull request was exported from Phabricator. Differential Revision: D52391695

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D52391695

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D52391695