Use menu behavior for add-highlighter/remove-highlighter completion

This means that typing

	:add-highlighter g c 80

results in

	:add-highlighter global/ column 80

Paths for add-highlighter do not get the menu behavior because we
want to be able to type "global/foo" even if "global/foobar" exists.

src/commands.cc

@@ -883,7 +883,8 @@ Completions highlighter_cmd_completer(
         StringView path = params[0];
         auto sep_it = find(path, '/');
         if (sep_it == path.end())
-           return { 0_byte, pos_in_token, complete(path, pos_in_token, highlighter_scopes) };
+           return { 0_byte, pos_in_token, complete(path, pos_in_token, highlighter_scopes),
+                    Completions::Flags::Menu };
 
         StringView scope{path.begin(), sep_it};
         HighlighterGroup* root = nullptr;
@@ -900,7 +901,8 @@ Completions highlighter_cmd_completer(
     else if (add and token_to_complete == 1)
     {
         StringView name = params[1];
-        return { 0_byte, name.length(), complete(name, pos_in_token, HighlighterRegistry::instance() | transform(&HighlighterRegistry::Item::key)) };
+        return { 0_byte, name.length(), complete(name, pos_in_token, HighlighterRegistry::instance() | transform(&HighlighterRegistry::Item::key)),
+                 Completions::Flags::Menu };
     }
     else
         return {};

src/highlighter_group.cc

@@ -75,7 +75,8 @@ Completions HighlighterGroup::complete_child(StringView path, ByteCount cursor_p
                        | transform([](auto& hl) { return hl.value->has_children() ? hl.key + "/" : hl.key; })
                        | gather<Vector<String>>());
 
-    return { 0, 0, std::move(candidates) };
+    auto completions_flags = group ? Completions::Flags::None : Completions::Flags::Menu;
+    return { 0, 0, std::move(candidates), completions_flags };
 }
 
 void Highlighters::highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange range)

src/highlighters.cc

@@ -2089,7 +2089,8 @@ public:
         }
 
         auto container = m_regions | transform(&decltype(m_regions)::Item::key);
-        return { 0, 0, complete(path, cursor_pos, container) };
+        auto completions_flags = group ? Completions::Flags::None : Completions::Flags::Menu;
+        return { 0, 0, complete(path, cursor_pos, container), completions_flags };
     }
 
     static std::unique_ptr<Highlighter> create(HighlighterParameters params, Highlighter*)