Avoid server action `endpoint` function indirection (#71572)
This PR removes the extra wrapper functions and `.bind()` calls from the
action entrypoint loader. Instead, the loader module now only re-exports
the actions from the original module using the IDs as export names. This
ensures that the same action instance will always remain identical. It
also unblocks the combined usage of `"use cache"` and `"use server"`
functions.
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Co-authored-by: Shu Ding <g@shud.in>
