Add KnownLayout::validate_cast_and_convert_metadata

This method is a core primitive that other parts of the codebase can
build on to validate casts and compute the appropriate pointer metadata
which should result from those casts. Future commits will build on top
of this one to make use of it.

Co-authored-by: Jack Wrenn <[email protected]>

Author: joshlf

Cargo.toml

@@ -55,6 +55,8 @@ optional = true
 zerocopy-derive = { version = "=0.7.3", path = "zerocopy-derive" }
 
 [dev-dependencies]
+assert_matches = "1.5"
+itertools = "0.11"
 rand = { version = "0.8.5", features = ["small_rng"] }
 rustversion = "1.0"
 static_assertions = "1.1"