Everywhere: Replace single-char StringView op. arguments with chars

This prevents us from needing a sv suffix, and potentially reduces the
need to run generic code for a single character (as contains,
starts_with, ends_with etc. for a char will be just a length and
equality check).

No functional changes.

Userland/Utilities/cpp-preprocessor.cpp

@@ -34,7 +34,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
             if (definition.value.parameters.is_empty())
                 outln("{}: {}", definition.key, definition.value.value);
             else
-                outln("{}({}): {}", definition.key, String::join(",", definition.value.parameters), definition.value.value);
+                outln("{}({}): {}", definition.key, String::join(',', definition.value.parameters), definition.value.value);
         }
         outln("");
     }

Userland/Utilities/diff.cpp

@@ -41,11 +41,11 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
 
         // Action
         if (num_added > 0 && num_removed > 0)
-            sb.append("c");
+            sb.append('c');
         else if (num_added > 0)
-            sb.append("a");
+            sb.append('a');
         else
-            sb.append("d");
+            sb.append('d');
 
         // Target line(s)
         sb.appendff("{}", target_start);

Userland/Utilities/js.cpp

@@ -1449,7 +1449,7 @@ public:
             return JS::js_undefined();
         }
 
-        auto output = String::join(" ", arguments.get<JS::MarkedVector<JS::Value>>());
+        auto output = String::join(' ', arguments.get<JS::MarkedVector<JS::Value>>());
         m_console.output_debug_message(log_level, output);
 
         switch (log_level) {

Userland/Utilities/mkdir.cpp

@@ -54,7 +54,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
         }
         StringBuilder path_builder;
         if (lexical_path.is_absolute())
-            path_builder.append("/");
+            path_builder.append('/');
 
         auto& parts = lexical_path.parts_view();
         size_t num_parts = parts.size();
@@ -88,7 +88,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
                     break;
                 }
             }
-            path_builder.append("/");
+            path_builder.append('/');
         }
     }
     return has_errors ? 1 : 0;

Userland/Utilities/mount.cpp

@@ -70,7 +70,7 @@ static int get_source_fd(StringView source)
 static bool mount_by_line(String const& line)
 {
     // Skip comments and blank lines.
-    if (line.is_empty() || line.starts_with("#"))
+    if (line.is_empty() || line.starts_with('#'))
         return true;
 
     Vector<String> parts = line.split('\t');

Userland/Utilities/stty.cpp

@@ -205,7 +205,7 @@ void print_human_readable(termios const& modes, winsize const& ws, bool verbose_
     auto escape_character = [&](u8 ch) {
         StringBuilder sb;
         if (ch <= 0x20) {
-            sb.append("^");
+            sb.append('^');
             sb.append(ch + 0x40);
         } else if (ch == 0x7f) {
             sb.append("^?"sv);

Userland/Utilities/telws.cpp

@@ -93,7 +93,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
         if (line.is_empty())
             continue;
 
-        if (line.starts_with(".")) {
+        if (line.starts_with('.')) {
             if (line.starts_with(".text "sv)) {
                 editor->add_to_history(line);
                 if (socket->ready_state() != Protocol::WebSocket::ReadyState::Open) {

Userland/Utilities/xargs.cpp

@@ -197,7 +197,7 @@ bool run_command(Vector<char*>&& child_argv, bool verbose, bool is_stdin, int de
 
     if (verbose) {
         StringBuilder builder;
-        builder.join(" ", child_argv);
+        builder.join(' ', child_argv);
         warnln("xargs: {}", builder.to_string());
     }
 

Userland/Utilities/xml.cpp

@@ -424,10 +424,10 @@ static void do_run_tests(XML::Document& document)
 
             StringBuilder path_builder;
             path_builder.append(base_path);
-            path_builder.append("/");
+            path_builder.append('/');
             for (auto& entry : bases.in_reverse()) {
                 path_builder.append(entry);
-                path_builder.append("/");
+                path_builder.append('/');
             }
             auto test_base_path = path_builder.to_string();