Refactor Recorder and improve API

[codemental]

The Recorder does not offer a clean API. Inside the Comparator we have calls like this:
AppendValidationErrorSignal("number of fields does not match") where the message is defined as a method parameter, and then we have methods like this inside the DefaultRecorder itself:
recorder.logResult.WriteString(fmt.Sprintf("%s <-- ignoring field\n", indent)).

It would be better for all methods to receive the jsonPath, fieldName and fieldValue from the comparator, and all messages (text) that are used to create the recorder log should be defined inside the Recorder implementation itself (in our case, the DefaultRecorder). This will offer a much cleaner way for other Recorder implementations to change the way the output looks and offer them full control.

Also, the Recorder uses fmt.Sprintf(...) internally in some cases which should not happen at all, since we are using a strings.Builder (!)

Action Points

• refactor API as mentioned above (I imagine we will have specific methods for different validation cases)
• remove the fmt.Sprintf(...) completely and only use the strings.Builder API
• write a dedicated test for the DefaultRecorder (currently it is tested inside the Comparator tests)