fix(ui5-popover): fix closing order of popovers

[fifoosid]

Fixes #1628

The problem was that there was no knowledge whether a popover is opened inside another popover and every time a popover was closed, all popovers on the whole page were closed. Now if a popover is closed only the popovers open within it are closed

[vladitasev]

I don't think we should do this. Traversing the DOM upwards and checking for a tag name is a prerequisite for many problems down the road. People can have their own popover-like components with different tag names, some might even not inherit from popover directly.

The point of the popup registry is to keep track of exactly this kind of information: whenever a new one opens, it registers itself, so we know which ones are below and which ones above. So to me the solution here is to completely use the registry.

[fifoosid]

I agree with the fact that traversing the DOM is not a good thing.

In the case when someone makes popover-like component, with different tag and/or not extending ui5-popover the current registry is NOT going to care of it as well, so from this POV we are not going to brake anything we have supported.

The current goal is to make each ui5-popover aware whether it is opened inside of another one or not.

[vladitasev]

Now Esc no longer closes subsequent popovers after you press it once. For example, in the case when you have 3 opening from one another, after you close the first one, nothing happens after you hit Esc for the second, or third time

[vladitasev]

I can approve, just fix the build.
Ohterwise, my comment is not so important, we can fix this later with the other change too.