PSA: Allowing data: URL redirects in fetch's manual redirect mode

[Helmut Januschka]

Hello,

This is an advance notice about an upcoming change that modifies how data: URL redirects are handled in the networking stack for Fetch requests using redirect: 'manual'.

This CL is a correctness fix to align with the Fetch Standard. It removes a restriction that currently blocks network requests when a 3xx redirect points to a `data:` URL under `redirect: 'manual'` mode. In this manual mode, the full redirect response (including the Location header) must be surfaced to the calling script (e.g., a Service Worker) for inspection, which the current restriction prevents. Standard `redirect: 'follow'` behavior is unchanged.

cheers,