Meta+Userland: Simplify some formatters

These are mostly minor mistakes I've encountered while working on the
removal of StringView(char const*). The usage of builder.put_string over
Format<FormatString>::format is preferrable as it will avoid the
indirection altogether when there's no formatting to be done. Similarly,
there is no need to do format(builder, "{}", number) when
builder.put_u64(number) works equally well.

Additionally a few Strings where only constant strings were used are
replaced with StringViews.

Userland/Libraries/LibGUI/PersistentModelIndex.h

@@ -86,8 +86,7 @@ struct Traits<GUI::PersistentModelIndex> : public GenericTraits<GUI::PersistentM
     {
         if (index.has_valid_handle())
             return Traits<GUI::ModelIndex>::hash(index.m_handle->m_index);
-        else
-            return 0;
+        return 0;
     }
 };