Flip include_chain_clauses_in_custom_matcher_descriptions default

From 3.1.0 changelog
(https://github.com/rspec/rspec-core/blame/main/Changelog.md#L773):

> the new rspec-expectations
> `include_chain_clauses_in_custom_matcher_descriptions` config option
> (which will be on by default in RSpec 4)

Changelog.md

@@ -7,6 +7,8 @@ Breaking Changes:
 * Extract `should*` (both monkey-patching and non-monkey-patching). (Phil Pirozhkov, #1245)
 * Remove deprecated `LegacyMacherAdapter`. (Phil Pirozhkov, #1253)
 * Remove support for legacy RSpec matchers (pre 3). (Phil Pirozhkov, #1253)
+* Change the default for `include_chain_clauses_in_custom_matcher_descriptions`
+  configuration option to `true`. (Phil Pirozhkov, #1253)
 
 Enhancements:
 

lib/rspec/expectations/configuration.rb

@@ -25,6 +25,7 @@ class Configuration
         }
 
       def initialize
+        @include_chain_clauses_in_custom_matcher_descriptions = true
         @on_potential_false_positives = :warn
         @strict_predicate_matchers = false
       end
@@ -86,10 +87,9 @@ def backtrace_formatter
       attr_writer :include_chain_clauses_in_custom_matcher_descriptions
 
       # Indicates whether or not custom matcher descriptions and failure messages
-      # should include clauses from methods defined using `chain`. It is
-      # false by default for backwards compatibility.
+      # should include clauses from methods defined using `chain`.
       def include_chain_clauses_in_custom_matcher_descriptions?
-        @include_chain_clauses_in_custom_matcher_descriptions ||= false
+        @include_chain_clauses_in_custom_matcher_descriptions
       end
 
       # @api private

spec/rspec/expectations/configuration_spec.rb

@@ -45,20 +45,20 @@ class << rspec_dup; undef configuration; end
       end
 
       describe "#include_chain_clauses_in_custom_matcher_descriptions?" do
-        it "is false by default" do
-          expect(config.include_chain_clauses_in_custom_matcher_descriptions?).to be false
-        end
-
-        it "can be set to true" do
-          config.include_chain_clauses_in_custom_matcher_descriptions = true
+        it "is true by default" do
           expect(config.include_chain_clauses_in_custom_matcher_descriptions?).to be true
         end
 
-        it "can be set back to false" do
-          config.include_chain_clauses_in_custom_matcher_descriptions = true
+        it "can be set to false" do
           config.include_chain_clauses_in_custom_matcher_descriptions = false
           expect(config.include_chain_clauses_in_custom_matcher_descriptions?).to be false
         end
+
+        it "can be set back to true" do
+          config.include_chain_clauses_in_custom_matcher_descriptions = false
+          config.include_chain_clauses_in_custom_matcher_descriptions = true
+          expect(config.include_chain_clauses_in_custom_matcher_descriptions?).to be true
+        end
       end
 
       describe "#max_formatted_output_length=" do