hexfloat: Deprecate to move out of the repo

This deprecates the hexfloat library as it is now located in the rust-lang
organization as a cargo package
Add examples for GenericPath methods.
Use byte strings throughout examples. Add an example that was missed in the last commit.
Add logic to skip the doc tests on windows since these examples are unix-specific
Byte literals!
Add a non-regression test for issue #8372
Deprecate semver.
Deprecate uuid.
Deprecate fourcc.
Remove incorrect example

This now works because of elision.

Fixes #16117
Add note about production deployments.

Fixes #11511.
librustc: Don't ICE when trying to subst regions in destructor call.
librustc: Don't ICE with struct exprs where the name is not a valid struct.
Implement slice::Vector for Option<T> and CVec<T>
alloc, arena, test, url, uuid: Elide lifetimes.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
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.)