Most of our transformers are pure compute and so don't really have a strong
need to generate trace spans under our current focus of only exposing
user-facing concepts and external requests in our traces, but unfortunately
some of them indirectly depend on provider schema, which in turn means that
they can potentially be unlucky enough to be the trigger for making all
of the provider requests needed to fill the schema cache and therefore
would end up with provider request spans being reported beneath them.
As usual with these interface updates, this initial change focuses only
on changing the interface and updating its direct callers and implementers
to match, without any further refactoring or attempts to plumb contexts
to or from other functions that don't have them yet. That means there are
a few new context.TODO() calls here that we'll tidy up in a later commit
that hopefully won't involve all of the noise that is caused by changing
an interface API.
Signed-off-by: Martin Atkins <mart@degeneration.co.uk>
