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 ()
[...]
```
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