wpf: Bump the history length to 9001 instead of 1000 (#15129)

This was an oversight in the original implementation.

src/cascadia/PublicTerminalCore/HwndTerminal.cpp

@@ -222,7 +222,7 @@ HRESULT HwndTerminal::Initialize()
 
     _renderEngine = std::move(dxEngine);
 
-    _terminal->Create({ 80, 25 }, 1000, *_renderer);
+    _terminal->Create({ 80, 25 }, 9001, *_renderer);
     _terminal->SetWriteInputCallback([=](std::wstring_view input) noexcept { _WriteTextToConnection(input); });
     localPointerToThread->EnablePainting();