Replace with terms and types

Let's set up some definitions to start:

.> builtins.merge

x = 1
y = 2

structural type X = One Nat
structural type Y = Two Nat Nat

.scratch> add

Test that replace works with terms

.scratch> replace x y
.scratch> view x

Test that replace works with types

.scratch> replace X Y
.scratch> find
.scratch> view.patch patch
.scratch> view X

Try with a type/term mismatch

.scratch> replace X x

.scratch> replace y Y

Try with missing references

.scratch> replace X NOPE

.scratch> replace y nope

.scratch> replace nope X

.scratch> replace nope y

.scratch> replace nope nope