fix: skip fs fallback for out of root urls, fix #3364

[patak-dev]

Description

Fix #3364, and other issues reported that were trying to access /service-worker.js.

This PR reworks the fs fallback check and skips it instead of failing with a security error if the URL results in a file access that is not allowed (ie out of workspace root for the moment, but later it could mean that it is present in a blocklist).

This change only applies when the user sets server.fsServe.strict to true

Additional context

The isFileAccessAllowed function may later contain more logic related to whitelist/blocklist so it is good that is already separated.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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