This PR adds a heterogeneous version of the constructor injectivity
theorems. These theorems are useful for indexed families, and will be
used in `grind`.
This PR generalizes the `noConfusion` constructions to heterogeneous
equalities (assuming propositional equalities between the indices). This
lays ground work for better support for applying injection to
heterogeneous equalities in grind.
The `Meta.mkNoConfusion` app builder shields most of the code from these
changes.
Since the per-constructor noConfusion principles are now more
expressive, `Meta.mkNoConfusion` no longer uses the general one.
In `Init.Prelude` some proofs are more pedestrian because `injection`
now needs a bit more machinery.
This is a breaking change for whoever uses the `noConfusion` principle
manually and explicitly for a type with indices.
Fixes#11450.
