Code Generation Documentation Tracking Issue

[jswrenn]

• Use examples requiring metadata fixup
• Use examples where fixed header size is not a power of two.
• Use examples with dynamic trailing padding.
• Include pretty-printed assembly.
• Use descriptive benchmark fn name, rather than codegen_test
• Include examples for most of zerocopy's API surface.
• Ensure codegen tests use pinned nightly tooling.
  • See Packages are selected by name, not ID pacak/cargo-show-asm#448