Make ActiveModel frozen string literal friendly.

Includes two external changes because they're referenced within the ActiveModel test suite.

actionpack/lib/action_dispatch/journey/router/utils.rb

@@ -29,7 +29,7 @@ class UriEncoder # :nodoc:
           ENCODE   = "%%%02X".freeze
           US_ASCII = Encoding::US_ASCII
           UTF_8    = Encoding::UTF_8
-          EMPTY    = "".force_encoding(US_ASCII).freeze
+          EMPTY    = "".dup.force_encoding(US_ASCII).freeze
           DEC2HEX  = (0..255).to_a.map { |i| ENCODE % i }.map { |s| s.force_encoding(US_ASCII) }
 
           ALPHA = "a-zA-Z".freeze

actionview/lib/action_view/helpers/javascript_helper.rb

@@ -13,8 +13,8 @@ module JavaScriptHelper
         "'"     => "\\'"
       }
 
-      JS_ESCAPE_MAP["\342\200\250".force_encoding(Encoding::UTF_8).encode!] = "
"
-      JS_ESCAPE_MAP["\342\200\251".force_encoding(Encoding::UTF_8).encode!] = "
"
+      JS_ESCAPE_MAP["\342\200\250".dup.force_encoding(Encoding::UTF_8).encode!] = "
"
+      JS_ESCAPE_MAP["\342\200\251".dup.force_encoding(Encoding::UTF_8).encode!] = "
"
 
       # Escapes carriage returns and single and double quotes for JavaScript segments.
       #

activemodel/test/cases/dirty_test.rb

@@ -96,7 +96,7 @@ def reload
   end
 
   test "attribute mutation" do
-    @model.instance_variable_set("@name", "Yam")
+    @model.instance_variable_set("@name", "Yam".dup)
     assert !@model.name_changed?
     @model.name.replace("Hadad")
     assert !@model.name_changed?

activemodel/test/cases/type/string_test.rb

@@ -14,7 +14,7 @@ class StringTest < ActiveModel::TestCase
       test "cast strings are mutable" do
         type = Type::String.new
 
-        s = "foo"
+        s = "foo".dup
         assert_equal false, type.cast(s).frozen?
         assert_equal false, s.frozen?