dillon1000/react

[Flight] Fallback to importing the whole module instead of encoding every name (#26624)

We currently don't just "require" a module by its module id/path. We
encode the pair of module id/path AND its export name. That's because
with module splitting, a single original module can end up in two or
more separate modules by name. Therefore the manifest files need to
encode how to require the whole module as well as how to require each
export name.

In practice, we don't currently use this because we end up forcing
Webpack to deopt and keep it together as a single module, and we don't
even have the code in the Webpack plugin to write separate values for
each export name.

The problem is with CJS we don't statically know what all the export
names will be. Since these cases will never be module split, we don't
really need to know.

This changes the Flight requires to first look for the specific name
we're loading and then if that name doesn't exist in the manifest we
fallback to looking for the `"*"` name containing the entire module and
look for the name in there at runtime.

We could probably optimize this a bit if we assume that CJS modules on
the server never get built with a name. That way we don't have to do the
failed lookup.

Additionally, since we've recently merged filepath + name into a single
string instead of two values, we now have to split those back out by
parsing the string. This is especially unfortunate for server references
since those should really not reveal what they are but be a hash or
something. The solution might just be to split them back out into two
separate fields again.

cc @shuding