This PR gives `#print` for structures the ability to show the default
values and auto-param tactics for fields.
Example:
```
#print Applicative
```
shows
```
class Applicative.{u, v} (f : Type u → Type v) : Type (max (u + 1) v)
[...]
fields:
Functor.map : {α β : Type u} → (α → β) → f α → f β :=
fun {α β} x y => pure x <*> y
Functor.mapConst : {α β : Type u} → α → f β → f α :=
fun {α β} => Functor.map ∘ Function.const β
Pure.pure : {α : Type u} → α → f α
Seq.seq : {α β : Type u} → f (α → β) → (Unit → f α) → f β
SeqLeft.seqLeft : {α β : Type u} → f α → (Unit → f β) → f α :=
fun {α β} a b => Function.const β <$> a <*> b ()
SeqRight.seqRight : {α β : Type u} → f α → (Unit → f β) → f β :=
fun {α β} a b => Function.const α id <$> a <*> b ()
[...]
```
This PR improves the `#print` command for structures to show all fields
and which parents the fields were inherited from, hiding internal
details such as which parents are represented as subobjects. This
information is still present in the constructor if needed. The pretty
printer for private constants is also improved, and it now handles
private names from the current module like any other name; private names
from other modules are made hygienic.
Example output for `#print Monad`:
```
class Monad.{u, v} (m : Type u → Type v) : Type (max (u + 1) v)
number of parameters: 1
parents:
Monad.toApplicative : Applicative m
Monad.toBind : Bind m
fields:
Functor.map : {α β : Type u} → (α → β) → m α → m β
Functor.mapConst : {α β : Type u} → α → m β → m α
Pure.pure : {α : Type u} → α → m α
Seq.seq : {α β : Type u} → m (α → β) → (Unit → m α) → m β
SeqLeft.seqLeft : {α β : Type u} → m α → (Unit → m β) → m α
SeqRight.seqRight : {α β : Type u} → m α → (Unit → m β) → m β
Bind.bind : {α β : Type u} → m α → (α → m β) → m β
constructor:
Monad.mk.{u, v} {m : Type u → Type v} [toApplicative : Applicative m] [toBind : Bind m] : Monad m
resolution order:
Monad, Applicative, Bind, Functor, Pure, Seq, SeqLeft, SeqRight
```
Suggested by Floris van Doorn [on
Zulip](https://leanprover.zulipchat.com/#narrow/channel/270676-lean4/topic/.23print.20command.20for.20structures/near/482503637).
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See RFC #3644 for a discussion of design choices.
Closes#3644
