Triggers completion window while still allowing processing by VsVim

Insert mode had a few issues. v2.8.0.8 fixed VsVim processing Insert mode keys but prevented the Intellisense window from appearing.

This fixes the 2.8.0.8 release by still allowing insert mode keys to be processed, but also triggering the Intellisense Window when needed.

Fixes #2832
Fixes #2844
Fixes #2807

Src/VimMac/VimKeyProcessor.cs

@@ -75,9 +75,32 @@ public override void KeyDown(KeyEventArgs e)
                 // Attempt to map the key information into a KeyInput value which can be processed
                 // by Vim.  If this works and the key is processed then the input is considered
                 // to be handled
+
                 if (_keyUtil.TryConvertSpecialToKeyInput(e.Event, out KeyInput keyInput))
                 {
+                    var bufferedKeyInputsWasEmpty = VimBuffer.BufferedKeyInputs.IsEmpty;
+
                     handled = TryProcess(keyInput);
+
+                    if (handled
+                        && BufferedKeysWasEmptyAndIsEmpty()
+                        && oldMode == ModeKind.Insert
+                        && CharTriggersCompletion(keyInput.Char)
+                        && !_completionBroker.IsCompletionActive(VimBuffer.TextView))
+                    {
+                        // Because VsVim handled the key press for us in insert mode,
+                        // we need to trigger the completion window to open.
+                        _completionBroker.TriggerCompletion(VimBuffer.TextView);
+                    }
+
+                    bool BufferedKeysWasEmptyAndIsEmpty()
+                    {
+                        // We don't want the completion window to appear if we
+                        // have something like `inoremap fd <esc>`
+                        // and we just typed the first 'f' or the 'd'
+                        return bufferedKeyInputsWasEmpty
+                        && VimBuffer.BufferedKeyInputs.IsEmpty;
+                    }
                 }
             }
 
@@ -94,6 +117,11 @@ public override void KeyDown(KeyEventArgs e)
             e.Handled = handled;
         }
 
+        private bool CharTriggersCompletion(char c)
+        {
+            return c == '_' || c == '.' || char.IsLetterOrDigit(c);
+        }
+
         /// <summary>
         /// Try and process the given KeyInput with the IVimBuffer.  This is overridable by 
         /// derived classes in order for them to prevent any KeyInput from reaching the