[READY] Handle scrolling when hover popup is open

[bstaletic]

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Why this change is necessary and useful

There are two kinds of scrolling that need to be handled:

1. Scrolling the buffer in a window shifts the buffer, but popups stay in place. Instead, we close the popup whenever we receive a WinScrolled event.
2. Scrolling the popup contents themselves resets the updatetime timer and can trigger a second CursorHold event, which leads to YCM resetting the hover popup. Instead, only re-display the hover popup if it is not already visible.

Open questions:

• Should we close other popups after WinScrolled?
• Tests... How do we even test "do X if mouse pointer at (x, y) position"? The behaviour differs when mouse pointer is inside or outside the popup area.

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This change is 

[codecov]

Codecov Report

Merging #4209 (cd48033) into master (05bbb07) will decrease coverage by 0.02%.
The diff coverage is 88.88%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4209      +/-   ##
==========================================
- Coverage   89.59%   89.58%   -0.02%     
==========================================
  Files          34       34              
  Lines        4440     4445       +5     
==========================================
+ Hits         3978     3982       +4     
- Misses        462      463       +1     

[puremourning]

Tests... How do we even test "do X if mouse pointer at (x, y) position"? The behaviour differs when mouse pointer is inside or outside the popup area.

there's a special vim function test_setmouse()

iirc you can also do feedkeys("\<MouseMove>") or something similar

Reviewable status: 0 of 2 LGTMs obtained

[bstaletic]

The test was working fine on my machine, but was inexplicably failing on CI. That's why I scrapped the test.

[puremourning]

Reviewed 1 of 1 files at r1, 1 of 1 files at r2, all commit messages.
Reviewable status: 1 of 2 LGTMs obtained (waiting on @bstaletic)

[mergify]

Thanks for sending a PR!