Make Symbol#to_s return frozen string.

Monkey-patch Symbol#to_s to return a frozen (immutable) string instead
of a mutable string.

This should reduce string allocations, and thereby reduce memory usage
and garbage collector pressure, but it may be incompatible with
libraries that expect Symbol#to_s to return a mutable string.

https://bugs.ruby-lang.org/issues/16150
https://github.com/Shopify/symbol-fstring

config/initializers/core_extensions.rb

@@ -62,3 +62,10 @@ end
 class String
   include Danbooru::Extensions::String
 end
+
+# Make Symbol#to_s return a frozen string. This reduces allocations, but may be
+# incompatible with some libraries.
+#
+# https://bugs.ruby-lang.org/issues/16150
+# https://github.com/Shopify/symbol-fstring
+Symbol.alias_method(:to_s, :name)