[libc++] [docs] Mark LWG3055 as complete. Use string_view instead of string in path::operator+=(ECharT).

[curdeius]

Summary

The issue didn't change the behaviour which is tested in libcxx/test/std/input.output/filesystems/class.path/path.member/path.concat.pass.cpp.

The change to use string_view instead of string is not strictly necessary.

<filesystem> was added in commit 998a5c88312066fcc2b2de1358edc76587611354 (Implement <filesystem>).

libcxx/docs/Cxx2aStatusIssuesStatus.csv

 "`3133 <https://wg21.link/LWG3133>`__","Modernizing numeric type requirements","Kona","",""
 "`3144 <https://wg21.link/LWG3144>`__","``span``\  does not have a ````const_pointer````\  typedef","Kona","|Complete|",""
 "`3173 <https://wg21.link/LWG3173>`__","Enable CTAD for *``ref-view``*\ ","Kona","",""
 "`3179 <https://wg21.link/LWG3179>`__","``subrange``\  should always model ``Range``\ ","Kona","",""
 "`3180 <https://wg21.link/LWG3180>`__","Inconsistently named return type for ``ranges::minmax_element``\ ","Kona","",""
 "`3182 <https://wg21.link/LWG3182>`__","Specification of ``Same``\  could be clearer","Kona","",""
 "","","","",""
 "`2899 <https://wg21.link/LWG2899>`__","``is_(nothrow_)move_constructible``\  and ``tuple``\ , ``optional``\  and ``unique_ptr``\ ","Cologne","",""
-"`3055 <https://wg21.link/LWG3055>`__","``path::operator+=(*single-character*)``\  misspecified","Cologne","",""
+"`3055 <https://wg21.link/LWG3055>`__","``path::operator+=(*single-character*)``\  misspecified","Cologne","|Complete|","7.0"
 "`3158 <https://wg21.link/LWG3158>`__","``tuple(allocator_arg_t, const Alloc&)``\  should be conditionally explicit","Cologne","",""
 "`3169 <https://wg21.link/LWG3169>`__","``ranges``\  permutation generators discard useful information","Cologne","",""
 "`3183 <https://wg21.link/LWG3183>`__","Normative permission to specialize Ranges variable templates","Cologne","",""
 "`3184 <https://wg21.link/LWG3184>`__","Inconsistencies in ``bind_front``\  wording","Cologne","",""
 "`3185 <https://wg21.link/LWG3185>`__","Uses-allocator construction functions missing ``constexpr``\  and ``noexcept``\ ","Cologne","",""
 "`3186 <https://wg21.link/LWG3186>`__","``ranges``\  removal, partition, and ``partial_sort_copy``\  algorithms discard useful information","Cologne","",""
 "`3187 <https://wg21.link/LWG3187>`__","`P0591R4 <https://wg21.link/p0591r4>`__ reverted DR 2586 fixes to ``scoped_allocator_adaptor::construct()``\ ","Cologne","",""
 "`3191 <https://wg21.link/LWG3191>`__","``std::ranges::shuffle``\  synopsis does not match algorithm definition","Cologne","",""

libcxx/include/filesystem

public:
   path& operator+=(value_type __x) {
     __pn_ += __x;
     return *this;
   }
 
   template <class _ECharT>
   typename enable_if<__can_convert_char<_ECharT>::value, path&>::type
   operator+=(_ECharT __x) {
-    basic_string<_ECharT> __tmp;
-    __tmp += __x;
-    _PathCVT<_ECharT>::__append_source(__pn_, __tmp);
+    _PathCVT<_ECharT>::__append_source(__pn_,
+                                       basic_string_view<_ECharT>(&__x, 1));
     return *this;
   }
 
   template <class _Source>
   _EnableIfPathable<_Source> operator+=(const _Source& __x) {
     return this->concat(__x);
   }