feat: add lcAny constant to Prelude (#6665)

This PR adds a new lcAny constant to Prelude, which is meant for use in
LCNF to represent types whose dependency on another term has been erased
during compilation. This is in addition to the existing lcErased
constant, which represents types that are irrelevant.

src/Init/Prelude.lean

@@ -150,6 +150,9 @@ It can also be written as `()`.
 /-- Marker for information that has been erased by the code generator. -/
 unsafe axiom lcErased : Type
 
+/-- Marker for type dependency that has been erased by the code generator. -/
+unsafe axiom lcAny : Type
+
 /--
 Auxiliary unsafe constant used by the Compiler when erasing proofs from code.