fix(datepicker): restore focus after closing popup

[maxokorokov]

At the moment the focus is lost, so it will be restored to the
previously focused element (before datepicker was opened)

Fixes #3317
Fixes #3358

[codecov-io]

Codecov Report

Merging #3371 into master will decrease coverage by 0.01%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master    #3371      +/-   ##
==========================================
- Coverage   90.88%   90.86%   -0.02%     
==========================================
  Files          95       95              
  Lines        2743     2748       +5     
  Branches      510      511       +1     
==========================================
+ Hits         2493     2497       +4     
  Misses        190      190              
- Partials       60       61       +1

Flag	Coverage Δ
#e2e	55.05% <80%> (+0.04%)	⬆️
#unit	87.94% <60%> (-0.06%)	⬇️

Impacted Files	Coverage Δ
src/datepicker/datepicker-input.ts	96.37% <80%> (-0.62%)	⬇️

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[peterblazejewicz]

It looks OK and this is welcome change!
There is one specific path I believe, this change could brake things (the use case with overlays with overlays, which are always tricky):

• open modal with datepicker
• open datepicker
• ESC key (currently keydown) to close

You should be able to see that modal behind datepicker dialog closes, not the datepicker alone.
This is probably due to the following:

• backing modal listens on keyup.ESC on the modal element, not on the document element
• dialog opens and delegates keydown.ESC to the document
• on the ESC key event modal handler catches first, closes the modal instance
• only after the modal handler finishes the autoclose fires the close on the datepicker, but its already too late.

Here is a fix for this, but it requires more changes:
https://gist.github.com/peterblazejewicz/2fc4a682e4ed1a56093ac04f7a67b480

• modal and dialog should listen on the same key, so if any of them catches event and do action, it could prevent event bubbling up (like in the keymap processors)
• the dialog picker should listen for the ESC event on its own, otherwise it delegates to the autoclose on the document
• the dialog stack should have a chance to prevent default and stop propagation, so the modal window handler has not.

Please see the gifs below with before/after this diff:

before:

after:

[maxokorokov]

@peterblazejewicz thanks for the review, you're right. Moreover it's the problem not only with the datepicker, but with all our components that are displayed inside the modal, ex. dropdown, typeahead. So I'd like to find a more generic solution for this problem

[maxokorokov]

Will merge this one as is and open another one to fix closing modal