DEV: Move saving of translations into base class

[nattsw]

Context

Since a long long time ago, we do the following in the Job::DetectTranslation:

discourse-translator/plugin.rb

Lines 126 to 130 in 4213639

	"DiscourseTranslator::#{SiteSetting.translator}".constantize.detect(post)
	if !post.custom_fields_clean?
	post.save_custom_fields
	post.publish_change_to_clients! :revised
	end

126. The first line, the method .detect has a side effect of assigning the detected language e.g. "en" into a custom field.
127. The subsequent lines in the job then saves the custom field.

The above is slightly confusing as there should be just one place that sets and saves the value. Additionally, the knowledge of the usage custom fields are in every subclass of the base translator.

Change

The following changes allow the saving of translation metadata to be in the single base class instead of sprinkled in all the subclasses. This is to prepare for the move from custom fields to proper tables.

This PR does two things:

1. introduce a detect! (and also translate!) in translator subclasses (Amazon, Google, Microsoft, etc) which will set the value from the API all the time. The base class invokes detect!.
   

   discourse-translator/app/services/discourse_translator/google.rb

   Lines 77 to 85 in 4c5d8e7

   	def self.detect!(topic_or_post)
   	save_detected_locale(topic_or_post) do
   	result(DETECT_URI, q: text_for_detection(topic_or_post))["detections"][0].max do |a, b|
   	a.confidence <=> b.confidence
   	end[
   	"language"
   	]
   	end
   	end

2. update detect to return the stored value or invoke the ! variant to get the value if it does not exist.
   

   discourse-translator/app/services/discourse_translator/base.rb

   Lines 51 to 57 in 4c5d8e7

   	# Returns the stored detected locale of a post or topic.
   	# If the locale does not exist yet, it will be detected first via the API then stored.
   	# @param topic_or_post [Post|Topic]
   	def self.detect(topic_or_post)
   	return if text_for_detection(topic_or_post).blank?
   	get_detected_locale(topic_or_post) || detect!(topic_or_post)
   	end

There is already test coverage for this refactor.

[nattsw]

This is moved to base.rb's save_detected_locale

[nattsw]

This is moved into base.rb so that all subclasses won't face the same issue.