It's good to create link to automatically report errors or suggest improvements to UI.

Could you elaborate why you think so? There are already many many links plus venues aren't always very clear and highly depend on the scope of an idea.
Plus if errors are automatically reported (to some extend they are in the Wikimedia infrastructure) there is no need for a link?

It should automatically fill the information needed in this context such as error message, browser version, username, article, filename, filesize, session id etc.

That might have privacy implications.

See related discussion and arguments in T111112, also when it comes to Sentry.

if there is a problem I am facing (as a reader or as an editor), I'd like to be able to report it. with all the details needed

Ok, as Antanana woke the task.
Sincerely I did not want to answer immediately, because I was very angry at MediaWiki developers and did not want to be overly emotional.
IMHO amount of bugs, severity and frequency of their appeance and amount of efforts required to properly design , implement and test the functionality (including thorough automated tests) in some components is largely neglected by WMF. I can (and did) write several pages of text to describe the details.

Also there is a lot inconveniencies in UI which can be improved by implementing some features.
Often people don't know that they can report or suggest somewhere. Often it's difficult to remember or thoroughfully fill the exact steps. Many issues come up when you have little time and ability to fill the information (Like when you are helping lots of students on Wikitraining or you desperate to finally (via buggy as usual upload wizard) upload photographs from recent event that you need to spread information in social media about). Or you are just angry when it happens and then forget as people tend to subdue negative emotions. If you see lots of bugs that are not fixed for a long time you may just feel you are not encouraged to report them unless you are presented with a prompt to do it.
Also developers told about many bugs that they cannot reproduce them (works for me!). Or that feedback pages flooded with unsatisfied reports are not constructive and helpfull because detailed steps are missing so no way to know how to reproduce it.
I largely believe these are just excuses or maybe they are not offered enough time by the management?
So I'd like either to provide the developers a better quality of details in bug reports as many users will not write perfect bug reports anyway or at least largely remove the excuse of not having that details :).

I understand that this feature needs a lot of work to implement properly and devotion to care about its output, not just to have another way to be silently and persistently ignored.

And I do not want to sound clever and belittle the WMF developers. We all have sins and difficulties. It's an idea to improve the software quality and relations with community.
I reported many bugs in Intellij Idea and I liked to be listened and to help the improve the software I use a lot (like Wikipedians use MediaWiki a lot (or sometimes struggle to))

As you also mention WMF initially, their plan is to have a product development process open to the participation of all communities. You can join the discussion about product development process and communication channels.

If you see lots of bugs that are not fixed for a long time you may just feel you are not encouraged to report them unless you are presented with a prompt to do it.

A prompt might create exactly the very same problem: Some annoying dialog that I just want to go away. (Plus it's unclear to me how and when such a prompt should even be triggered.)

Also developers told about many bugs that they cannot reproduce them (works for me!).

That's true but I don't see how automated error reporting would help much. Plus privacy (browser, browser settings, operating system, provider ...) might collide.

Or that feedback pages flooded with unsatisfied reports are not constructive and helpfull because detailed steps are missing so no way to know how to reproduce it.

Automated error reporting will not magically provide steps to reproduce...

Is this related to T29852: Wikimedia wikis need better issue reporting system?

Server-side errors have been logged (and exposed to all developers via logstash) for a long time. (Could use improvements, see e.g. T157850: Interacting with Wikimedia logs should be a pleasant experience, but then so could everything else.)
For client-sider error reporting, see the Sentry project (stalled mostly due to lack of resources and relatively limited interest from developers).
There are a few things that fall inbetween (such as image load errors in MediaViewer, for which we tried to create a reporting system but as you can see from T111112#1902734 it didn't really prove useful).

This task seems to have been written with crash reporting systems in mind. Those are a lot less useful for web applications then for desktop apps.