`didClose` and `didOpen` events go out of balance when dragging an editor window from the main IDE view to another view

The out-of-balance causes similar problems to #574.

"Dragging an editor window from the main IDE view to another view" is shown below.

This is the initial state of the main IDE view:

After dragging file2.py out to another IDE view:

This dragging event only triggers a single textDocument/didClose event, so the language server now thinks file2.py is closed.

[Trace - 09:42:09] Sending notification 'textDocument/didClose'

For this particular example, where only one file2.py view is present, I expected either one of these after dragging:

• Neither didClose nor didOpen events should trigger
• Both didClose and didOpen events should trigger

However, in the scenario where there was another open editor window of file2.py (so 2 or more views of file2.py in total), then dragging file2.py out should not trigger any didOpen or didClose events (currently, LSP4IJ behaves correctly in this scenario).

I do not know when this problem started occurring; it may have started before the latest release of LSP4IJ. This bug reproduction is for the latest release (v0.18).

Reproduce the issue in LSP4IJ v0.18 by dragging file2.py from the main IDE view to another view, and inspect the textDocument/didOpen and textDocument/didClose trace. Done means the move no longer leaves the language server believing the file is closed, while the behavior remains correct when multiple views of file2.py are open.