add a tag diff to /(node|way|relation)/:id/history

[stillhart]

Description

I added a tag diff between change sets to highlight the changes of tags.

The diff is not expanded by default. I wanted the diff in between the change sets to avoid confusion with the given state at that time. I wanted the diff to be opt-in.
I used the default bootstrap colors which contrasts many other implementations.
I didn't want any strike through text.

Relates to #738 #1253 #4765

Screenshots

Expanded

Without expansion

How has this been tested?

• I ran the (new) tests
  • docker compose exec web bundle exec rails test test/system/element_history_test.rb test/helpers/browse_tags_helper_test.rb
• I tested it manually on my docker instance

What should be discussed?

1. It won't show a diff across pagination since I didn't want to mess with record loading. This is by design at the moment. Could be added by just giving the record to the partial.
2. Design is ok but somewhat lacking, but is using the existing bootstrap design.
3. I tried to be screen reader friendly since colors are not obvious, but I'm not certain about that.
4. I don't like the text Tag changes from version #1 to #2 all that much.
5. Additions green, removals red, but modifications could also be two shades of blue. Or two other shades of green and red.
6. Naming of the two change sets might need improvement inside the code:
   • old new
   • previous next
   • before after

None of the above seem to be deal breakers for me.

Note: I was AI assisted.

[stillhart]

Just came across #6448. That one has kinda nicer styling but I don't like the "in change set view". Mine seems to be a different approach. An obvious diff that is explicitly in between the two affected records.

[tomhughes]

As you have apparently now discovered there is already a well developed PR working on this that has had a number of rounds of review so I think it's likely that is the best place to be working on things.

[1ec5]

An obvious diff that is explicitly in between the two affected records.

Maybe that could go on a separate page that’s dedicated to diffing two versions of an element, as in #6761? That could be in addition to what’s going on in #6448.