Clean layout after `tabclose`

[przepompownia]

Hi, this bug exists as long as we introduced expanding long lines but I did not found time to show the reproduction.

Given https://github.com/przepompownia/dap-ui-test run make line-hover-extmarks-after-tabclose and notice that extmarks are not shown up.

In short, after tabclose we can still find buffers used to create UI:

:au DAPUIExpandLongLinesForStacks
--- Autocommands ---
DAPUIExpandLongLinesForStacks  CursorMoved
    <buffer=8>
              <Lua function 46>
DAPUIExpandLongLinesForStacks  WinScrolled
    <buffer=8>
              <Lua function 46>
Press ENTER or type command to continue

In the above example, if we unhide such orphan buffer (:sb 8) into the layout, then we can observe that the old works but its new equivalent - not.

Given this knowledge the user have to run dapui.close() before tabclose to make this cleaning at the user side while it is not performed by dap-ui.