rustdoc: Feature request: Also render the alignment under `--show-type-layout`

Problem

It can be tedious to query the size/alignment of non-generic types (struct, enum, union), which one might want to do for many reasons. Currently, you have to do one of the following:

1. Compile a crate that has access to the type in question and print the value.
2. Print the value from the playground, if the crate is available there (which probably wont be the case for anything you're currently working on.)
3. Inspect compiler output via -Zprint-type-sizes.

All of these have the problem of having to compile code to get an answer.

Proposed Solution

The ideal solution would be to display the size & alignment of types in the cargo doc generated output, so you wouldn't have to build a crate.

Notes

I have no idea how feasible this is, but given that cargo doc already compiles and runs doc tests, it doesn't seem unreasonable.

Start by examining rustdoc's existing --show-type-layout behavior and compare it with compiler output from -Zprint-type-sizes. Trace how cargo doc renders type layout information. Done means cargo doc output reports both size and alignment for non-generic structs, enums, and unions without requiring extra code to be compiled.