Adds hover-highlighting for relations in the raw membership list

[quincylvania]

Also:

• Moves hover-highlighting behavior to its own function
• Hover-highlighting now correctly highlights all members of the target relation

Completes task 1 of #2946. Continuation of #5402 and #5404.

@bhousel Adding recursive highlighting for relations meant that the code snippet became too large to keep repeating everywhere, so I moved the highlighting logic to its own file/function. I'd like guidance on the naming and location of this file.

[bhousel]

@bhousel Adding recursive highlighting for relations meant that the code snippet became too large to keep repeating everywhere, so I moved the highlighting logic to its own file/function. I'd like guidance on the naming and location of this file.

I'd put the highlighting code in https://github.com/openstreetmap/iD/blob/master/modules/util/util.js
or in its own file under util. (maybe reusing some of the code in util.js is there already).

The convention we follow is if the function is named utilSomethingSomething, the file should be util/something_something.js

👉 Also, relations are tricky and can be circular (a relation can contain itself or an ancestor as a child), so it's really best to avoid recursing. e.g. utilGetAllNodes uses a seen variable to avoid infinite looping: https://github.com/openstreetmap/iD/blob/master/modules/util/util.js#L44

[quincylvania]

@bhousel Thanks for the tip on circular relations! I hadn't considered those were possible. I made some changes, let me know if you have further suggestions. Otherwise it's ready.

[bhousel]

Looks great, thanks!