Customizing content completion item in Author mode

[raducoravu]

Converted from internal issue: EXM-42806
Based on this answer:
https://www.oxygenxml.com/forum/post51575.html#p51575

[raducoravu]

Un alt caz asemanator aici la care a raspuns @AlexJitianu :
https://www.oxygenxml.com/forum/viewtopic.php?p=57446#p57446

[raducoravu]

@AlexJitianu if you want and have the time maybe you can write the blog post.

[raducoravu]

One more case here:
https://www.oxygenxml.com/forum/post57579.html#p57579

[raducoravu]

One more usecase:
https://www.oxygenxml.com/forum/viewtopic.php?p=57589#p57589

[raducoravu]

@StevenHiggs maybe when you have the time you could review my topic:
https://blog.oxygenxml.com/topics/custom-author-action-content-completion.html