Fix one source of mouse vanishing (#18911)

When the cursor is over the non-client area it wouldn't
show the cursor when moving it. Now it works as expected.

(cherry picked from commit 4d094df)
Service-Card-Id: PVTI_lADOAF3p4s4AxadtzgaZJvk
Service-Version: 1.23

Author: lhecker

.github/actions/spelling/allow/apis.txt

@@ -144,6 +144,7 @@ NCHITTEST
 NCLBUTTONDBLCLK
 NCMOUSELEAVE
 NCMOUSEMOVE
+NCPOINTERUPDATE
 NCRBUTTONDBLCLK
 NIF
 NIN

src/cascadia/WindowsTerminal/IslandWindow.cpp

@@ -61,7 +61,10 @@ void IslandWindow::HideCursor() noexcept
 
 void IslandWindow::ShowCursorMaybe(const UINT message) noexcept
 {
-    if (_cursorHidden && (message == WM_ACTIVATE || message == WM_POINTERUPDATE))
+    if (_cursorHidden &&
+        (message == WM_ACTIVATE ||
+         message == WM_POINTERUPDATE ||
+         message == WM_NCPOINTERUPDATE))
     {
         _cursorHidden = false;
         ShowCursor(TRUE);