Make `simd` and `simd_mask` ranges

[someonewithpc]

version / revision	Operating System	Compiler & Version	Compiler Flags	CPU
?	All	All	All	All

Motivation

The library already provides indexed access. Providing a range interface/iterator access would allow the type to be used with all STL functions. Event though it would degrade to doing it element-wise, it would still vastly increase the ergonomics when some specific utility is not directly available for the simd type. It could also pave the way for specializing some STL functions, like std::min_element, instead of providing hmin, addressing #18

Let me know if you think this is a direction worth taking and I can write a PR

Testcase

#include <experimental/simd>
#include <iostream>

namespace stdx = std::experimental;

int main() {
  stdx::native_simd<int> a{[](int i) { return 2 << (i - 1); }};

  for (auto v : a) {
    std::cout << v << '\n';
  }
}

Actual Results

$ g++ simd-range.cpp && ./a.out 
simd-range.cpp: In function ‘int main()’:
simd-range.cpp:13:17: error: ‘begin’ was not declared in this scope; did you mean ‘std::begin’?
   13 |   for (auto v : a) {
      |                 ^
      |                 std::begin
In file included from /usr/include/c++/13.2.1/string:53,
                 from /usr/include/c++/13.2.1/bitset:52,
                 from /usr/include/c++/13.2.1/experimental/bits/simd.h:33,
                 from /usr/include/c++/13.2.1/experimental/simd:74,
                 from simd-range.cpp:1:
/usr/include/c++/13.2.1/bits/range_access.h:114:37: note: ‘std::begin’ declared here
  114 |   template<typename _Tp> const _Tp* begin(const valarray<_Tp>&) noexcept;
      |                                     ^~~~~
simd-range.cpp:13:17: error: ‘end’ was not declared in this scope; did you mean ‘std::end’?
   13 |   for (auto v : a) {
      |                 ^
      |                 std::end
/usr/include/c++/13.2.1/bits/range_access.h:116:37: note: ‘std::end’ declared here
  116 |   template<typename _Tp> const _Tp* end(const valarray<_Tp>&) noexcept;
      | 

Expected Results

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