rustc: Improve type size assertions

Now they
- Tell what the new size is, when it changes
- Do not require passing an identifier

```
   ::: src\libsyntax\parse\token.rs:223:1
    |
223 |    static_assert_size!(Token, 123);
    |    -------------------------------- in this macro invocation
    |
    = note: expected type `[(); 123]`
               found type `[(); 16]`
```

Rollup of 11 pull requests

Successful merges:

 - #60383 (Fix position source code files toggle)
 - #60453 (Fall back to `/dev/urandom` on `EPERM` for `getrandom`)
 - #60487 (Fix search sidebar width when no crate select is present)
 - #60511 (Fix intra-doc link resolution failure on re-exporting libstd)
 - #60823 (Fix incremental compilation of cdylib emitting spurious unused_attributes lint)
 - #60915 (stable hashing: Remove unused field and add documentation.)
 - #60942 (Misc changes to rustc_metadata)
 - #60952 (Document BinaryHeap time complexity)
 - #60959 (rustc: Improve type size assertions)
 - #60972 (remove confusing remarks about mixed volatile and non-volatile accesses)
 - #60983 (Set -funwind-tables and -fno-exceptions unconditionally for LLVM's libunwind)

Failed merges:

r? @ghost