Simplify Flight manifest plugin (#51589)
Instead of traversing the entire client module graph twice (!), this PR
changes it to only traverse the client **entry** modules only. Because
of the way we create client entries, all client modules' _boundaries_
can be retrieved via all outgoing connections of all chunks' entry
modules, filtered by `next-flight-client-entry-loader`.
This brings down the time complexity from `2 * num_client_modules` to
`num_client_entry_modules`.
Closes #51240.
Additional notes from @timneutkens
- Removed `module.unsafeCache` as it seemed to be leaking modules across
multiple compilations, this should help with memory usage
- Changed entry-loader to have consistent module import map (sort it) to
ensure cache key is consistent
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Co-authored-by: Tim Neutkens <tim@timneutkens.nl>
