Test fixes from the rollup

Closes #16097 (fix variable name in tutorial)
Closes #16100 (More defailbloating)
Closes #16104 (Fix deprecation commment on `core::cmp::lexical_ordering`)
Closes #16105 (fix formatting in pointer guide table)
Closes #16107 (remove serialize::ebml, add librbml)
Closes #16108 (Fix heading levels in pointer guide)
Closes #16109 (rustrt: Don't conditionally init the at_exit QUEUE)
Closes #16111 (hexfloat: Deprecate to move out of the repo)
Closes #16113 (Add examples for GenericPath methods.)
Closes #16115 (Byte literals!)
Closes #16116 (Add a non-regression test for issue #8372)
Closes #16120 (Deprecate semver)
Closes #16124 (Deprecate uuid)
Closes #16126 (Deprecate fourcc)
Closes #16127 (Remove incorrect example)
Closes #16129 (Add note about production deployments.)
Closes #16131 (librustc: Don't ICE when trying to subst regions in destructor call.)
Closes #16133 (librustc: Don't ICE with struct exprs where the name is not a valid struct.)
Closes #16136 (Implement slice::Vector for Option<T> and CVec<T>)
Closes #16137 (alloc, arena, test, url, uuid: Elide lifetimes.)