STL: Mark simple casting free functions with `_MSVC_INTRINSIC`

[frederick-vs-ja]

#3182 added [[msvc::intrinsic]] attribute to the following reference-casting function templates:

• forward
• forward_like
• move
• move_if_noexcept

, which made MSVC treat a call to such a function equivalent to a simple static_cast.

Per local verifications and response from Cameron DaCamara (@cdacamar) on Discord, it works for free functions which is equivalent to a cast. Here is an incomplete list of such functions, including internal helpers, in MSVC STL:

• Reference casting functions (I've verified locally some of them and believe [[msvc::intrinsic]] works)
  • as_const (in <utility>)
  • _Possibly_const_range (in <xutility>)
  • _As_lvalue (in <ranges>)
• Pointer casting functions (seemly works, but not very sure)
  • _As_const_pointer (in <xutility>)
• Integer/enumeration casting functions (seemly works, but not very sure)
  • to_integer (in <cstddef>)
  • to_underlying (in <utility>)

It would be great to find all of these functions and mark them with _MSVC_INTRINSIC.

Note that the [[msvc::intrinsic]] attribute currently doesn't work for member functions (both non-static and static ones), so even though identity::operator() looks like a good candidate, it's better not to mark it with _MSVC_INTRINSIC at this moment.

Jakub Mazurkiewicz (@JMazurkiewicz) suggested that this might be a nice candidate for "good first issue".

[StephanTLavavej]

The actual changes will be good-first-issue material, but the need to do a global audit is beyond what we typically consider such an issue.

[frederick-vs-ja]

_As_lvalue is somehow problematic and not yet suitable for [[msvc::intrinsic]] in 17.7 Preview 3.