(maint) Refactor Sidecar Protocol serialisation

Previously the Sidecar Protocol had the serialisation methods on the
BasePuppetObject however this meant anything that wanted to use the
serialisation methods also inherited the parameters like key and calling_source.

This commit:
* Moves the serialisation methods (to_json, from_json!) to BaseClass which
  BasePuppetObject now inherits from
* Adds equality methods on the BaseClass to make it possible to compare
  Sidecar objects correctly.  This is mainly required in spec tests to test for
  equality (either == or eql?)
* Adds a hash method to generate the hash number required when Sidecar objects
  are put into hashtables

There are no test changes as this is a refactor only.

lib/puppet-languageserver/sidecar_protocol.rb

@@ -29,14 +29,61 @@ def from_json!(json_string)
         end
       end
 
+      class BaseClass
+        include Base
+
+        def to_json(*options)
+          to_h.to_json(options)
+        end
+
+        def from_json!(json_string)
+          from_h!(JSON.parse(json_string))
+        end
+
+        def ==(other)
+          return false unless other.class == self.class
+          self.class
+              .instance_methods(false)
+              .reject { |name| name.to_s.end_with?('=') || name.to_s.end_with?('!') }
+              .reject { |name| %i[to_h to_json].include?(name) }
+              .each do |method_name|
+            return false unless send(method_name) == other.send(method_name)
+          end
+          true
+        end
+
+        def eql?(other)
+          return false unless other.class == self.class
+          self.class
+              .instance_methods(false)
+              .reject { |name| name.to_s.end_with?('=') || name.to_s.end_with?('!') }
+              .reject { |name| %i[to_h to_json].include?(name) }
+              .each do |method_name|
+            return false unless send(method_name).eql?(other.send(method_name))
+          end
+          true
+        end
+
+        def hash
+          props = []
+          self.class
+              .instance_methods(false)
+              .reject { |name| name.to_s.end_with?('=') || name.to_s.end_with?('!') }
+              .reject { |name| %i[to_h to_json].include?(name) }
+              .each do |method_name|
+            props << send(method_name).hash
+          end
+          props.hash
+        end
+      end
+
       # key            => Unique name of the object
       # calling_source => The file that was invoked to create the object
       # source         => The file that _actually_ created the object
       # line           => The line number in the source file where the object was created
       # char           => The character number in the source file where the object was created
       # length         => The length of characters from `char` in the source file where the object was created
-      class BasePuppetObject
-        include Base
+      class BasePuppetObject < BaseClass
         attr_accessor :key
         attr_accessor :calling_source
         attr_accessor :source
@@ -64,14 +111,6 @@ def from_h!(value)
           self.length         = value['length']
           self
         end
-
-        def to_json(*options)
-          to_h.to_json(options)
-        end
-
-        def from_json!(json_string)
-          from_h!(JSON.parse(json_string))
-        end
       end
 
       class BasePuppetObjectList < Array