Make utf8_iterator a proper stl useable iterator

src/keys.cc

@@ -53,8 +53,7 @@ KeyList parse_keys(StringView str)
             continue;
         }
 
-        Utf8It end_it = it;
-        skip_while(end_it, str_end, [](char c) { return c != '>'; });
+        Utf8It end_it = std::find(it, str_end, '>');
         if (end_it == str_end)
         {
             result.push_back({Key::Modifiers::None, *it});

src/normal.cc

@@ -727,8 +727,7 @@ void join_lines_select_spaces(Context& context, NormalParams)
         for (LineCount line = min_line; line < end_line; ++line)
         {
             auto begin = buffer.iterator_at({line, buffer[line].length()-1});
-            auto end = begin+1;
-            skip_while(end, buffer.end(), is_horizontal_blank);
+            auto end = std::find_if_not(begin+1, buffer.end(), is_horizontal_blank);
             selections.push_back({begin.coord(), (end-1).coord()});
         }
     }

src/utf8_iterator.hh

@@ -3,6 +3,8 @@
 
 #include "utf8.hh"
 
+#include <iterator>
+
 namespace Kakoune
 {
 
@@ -13,7 +15,8 @@ namespace utf8
 // on unicode codepoints instead.
 template<typename Iterator,
          typename InvalidPolicy = utf8::InvalidPolicy::Pass>
-class iterator
+class iterator : public std::iterator<std::forward_iterator_tag,
+                                      Codepoint, CharCount>
 {
 public:
     iterator() = default;