Add a total order on type constructors

Several proposals for ExtensibleRecords can be implemented as libraries if type constructors can be ordered globally.

This proposal is to add built-in types:

data LabelLT
data LabelEQ
data LabelGT
type family LabelCMP

such that, for any two datatypes

data N = N
data M = M

the instance LabelCMP N M takes one of the values LabelLT, LabelEQ, LabelGT depending on the lexicographic ordering on the fully-qualified names of N and M.

Trac metadata

Trac field	Value
Version	6.8.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Multiple
Architecture	Multiple