Local variable access was originally broken, reportedly, in Rails 5.1
in d6bac046 which dropped the `locals` keys from some of the layout
lookup methods to optimize the template resolver cache.

In the meantime, the template resolver cache was discarded in Rails
7.0 in 4db7ae52, and was replaced by a FileSystemResolver cache that
does not use the locals in the lookup key (because it's storing
unbound templates).

So this fix is, essentially, to once again pass the local variable
names through the many layers of the layout resolver/renderer stack to
make sure that when the unbound template is found and `#bind_locals`
is called on it, it's bound with the proper set of local variable
names.

Fixes #31680