This PR does some refactoring of the function application elaborator,
and it improves `trace.Elab.app` tracing. It also improves asymptotic
complexity by more carefully substituting arguments into the function's
type and by changing how named argument dependency suppression is
implemented. For dot notation, it now constructs base projections
directly rather than using the app elaborator. It fixes a bug in the eta
args feature where more explicit arguments would be turned into implicit
arguments than expected, and it improves expected type propagation by
following the rules from the main app elaborator.
5d22886aff