Improve documentation of RecordNotSaved and RecordNotDestroyed [ci-skip]

Add examples and explain that RecordNotDestroyed triggered by throwing
:abort in callbacks.

Co-authored-by: Carlos Antonio da Silva <[email protected]>

Author: p8

activerecord/lib/active_record/errors.rb

@@ -130,9 +130,17 @@ def initialize(message = nil, model = nil, primary_key = nil, id = nil)
 
   # Raised by {ActiveRecord::Base#save!}[rdoc-ref:Persistence#save!] and
   # {ActiveRecord::Base.update_attribute!}[rdoc-ref:Persistence#update_attribute!]
-  # methods when a record is failed to validate or cannot be saved due to any of the
+  # methods when a record failed to validate or cannot be saved due to any of the
   # <tt>before_*</tt> callbacks throwing +:abort+. See
-  # ActiveRecord::Callbacks for further details
+  # ActiveRecord::Callbacks for further details.
+  #
+  #   class Product < ActiveRecord::Base
+  #     before_save do
+  #       throw :abort if price < 0
+  #     end
+  #   end
+  #
+  #   Product.create! # => raises an ActiveRecord::RecordNotSaved
   class RecordNotSaved < ActiveRecordError
     attr_reader :record
 
@@ -143,15 +151,17 @@ def initialize(message = nil, record = nil)
   end
 
   # Raised by {ActiveRecord::Base#destroy!}[rdoc-ref:Persistence#destroy!]
-  # when a call to {#destroy}[rdoc-ref:Persistence#destroy]
-  # would return false.
+  # when a record cannot be destroyed due to any of the
+  # <tt>before_destroy</tt> callbacks throwing +:abort+. See
+  # ActiveRecord::Callbacks for further details.
   #
-  #   begin
-  #     complex_operation_that_internally_calls_destroy!
-  #   rescue ActiveRecord::RecordNotDestroyed => invalid
-  #     puts invalid.record.errors
+  #   class User < ActiveRecord::Base
+  #     before_destroy do
+  #       throw :abort if still_active?
+  #     end
   #   end
   #
+  #   User.first.destroy! # => raises an ActiveRecord::RecordNotDestroyed
   class RecordNotDestroyed < ActiveRecordError
     attr_reader :record