GraphicContext: Use std::stack with a std::vector

Every frame the `m_transforms` is filled and emptied. By default the
`std::stack` uses a `std::deque` which releases its memory when it shrinks.
This causes constant allocations and deallocations. With a `std::vector`
this doesn't happen.

Author: neo1973

xbmc/windowing/GraphicContext.h

@@ -270,7 +270,7 @@ class CGraphicContext : public CCriticalSection
 
   UITransform m_guiTransform;
   UITransform m_finalTransform;
-  std::stack<UITransform> m_transforms;
+  std::stack<UITransform, std::vector<UITransform>> m_transforms;
   RENDER_STEREO_VIEW m_stereoView = RENDER_STEREO_VIEW_OFF;
   RENDER_STEREO_MODE m_stereoMode = RENDER_STEREO_MODE_OFF;
   RENDER_STEREO_MODE m_nextStereoMode = RENDER_STEREO_MODE_OFF;