Everywhere: Add sv suffix to strings relying on StringView(char const*)

Each of these strings would previously rely on StringView's char const*
constructor overload, which would call __builtin_strlen on the string.
Since we now have operator ""sv, we can replace these with much simpler
versions. This opens the door to being able to remove
StringView(char const*).

No functional changes.

Userland/Libraries/LibMarkdown/HorizontalRule.cpp

@@ -22,7 +22,7 @@ String HorizontalRule::render_for_terminal(size_t view_width) const
     StringBuilder builder(view_width + 1);
     for (size_t i = 0; i < view_width; ++i)
         builder.append('-');
-    builder.append("\n\n");
+    builder.append("\n\n"sv);
     return builder.to_string();
 }