Tracking issue for Lazy Normalization of Constants

[nikomatsakis]

As a subpart of #60471, this tracks the work around normalizing constants that began with #71973.

Background and links to reading material

There is a hackmd that sketched out some notes and a basic plan, though it's evolved some since then.

FIXMEs and issues to be resolved

• Detection of illegal regions in opaque types for constants
• Diagnostics for mismatched types
• Post lazy normalization for consts cleanup (#71973) #72129 misc cleanup

[lcnr]

cc #72129

[lcnr]

Lazy normalization of constants can be experimented with by either using #![feature(const_generics)] or just #![feature(lazy_normalization_consts)].