Show source view and backtrace on missing template errors

This will help you debug missing template errors, especially if they
come from a programmatic template selection. Thanks to @dhh for
suggesting that.

As a bonus, also show request and response info on the routing error
page for consistency.
Merge pull request #17747 from gsamokovarov/missing-template-backtrace

Show source view and backtrace on missing template errors