feat(events): add DirChangedPre

In Nvim, like DirChanged, this also triggers when switching windows.

This marks Vim patch 8.2.4335 as ported.

vim-patch:8.2.4335: no autocommand event triggered before changing directory

Problem:    No autocommand event triggered before changing directory. (Ronnie
            Magatti)
Solution:   Add DirChangedPre. (closes vim/vim#9721)
28e8f73ae2

src/nvim/auevents.lua

@@ -40,6 +40,7 @@ return {
     'DiagnosticChanged',      -- diagnostics in a buffer were modified
     'DiffUpdated',            -- diffs have been updated
     'DirChanged',             -- directory changed
+    'DirChangedPre',          -- directory is going to change
     'EncodingChanged',        -- after changing the 'encoding' option
     'ExitPre',                -- before exiting
     'FileAppendCmd',          -- append to a file using command
@@ -132,18 +133,14 @@ return {
   nvim_specific = {
     BufModifiedSet=true,
     DiagnosticChanged=true,
-    DirChanged=true,
     RecordingEnter=true,
     RecordingLeave=true,
     Signal=true,
-    TabClosed=true,
-    TabNew=true,
     TabNewEntered=true,
     TermClose=true,
     TermOpen=true,
     UIEnter=true,
     UILeave=true,
-    WinClosed=true,
     WinScrolled=true,
   },
 }