fix(window): clear docs popup when menu updates to prevent stale items

[soifou]

Problem: documentation popup could stick around and leave "dead" window on screen when the menu updates completion items.

Solution: ensures the doc window closes when the menu updates.

Closes #1932

[Saghen]

We'll close the documentation if the menu closes here:

blink.cmp/lua/blink/cmp/completion/windows/documentation.lua

Line 42 in fe7c974

menu.close_emitter:on(function() docs.close() end)

From the attached video in #1932, it looks like the menu is sticking around but only the bottom half of it. Maybe there's a weird rendering bug happening