API Use class from new template engine module

[GuySartorelli]

The template engine code is in its own module now, so we need to add it as a dependency and update the use statement. Going with API since that feels like it takes precedence over DEP and updating a use statement feels like a API commit to me, but I'm happy to change the prefix if the reviewer wants me to.

I couldn't think of a clean way to easily abstract this out, given it intentionally uses the same configuration that template partial caching uses, and that is a concept specific to ss templates that can't be abstracted to be for generic template engines.

I think it's sensible to leave this as a strict dependency for now given we have strong coupling to this template engine for all of the CMS templates anyway. If we ever make a move to decouple from the module, we can take another look here at that time - that would need to happen in a future major release anyway since it would mean (at a minimum) moving our CMS templates out of their current modules.

CI for this can't go green until silverstripe/silverstripe-framework#11451 has been merged

Issue

• Abstract template layer into its own dedicated module silverstripe-framework#11322