GPU: Clamp coordinates to 11 bits after applying drawing offset

Fixes flickering in some scenes (e.g. Galbadia Missile Base).

src/core/gpu.h

@@ -251,10 +251,15 @@ protected:
   {
     u32 bits;
 
-    BitField<u32, s32, 0, 12> x;
-    BitField<u32, s32, 16, 12> y;
+    BitField<u32, s32, 0, 11> x;
+    BitField<u32, s32, 16, 11> y;
   };
 
+  // Vertices have to be clamped to 11 bits before rendering. Normally this would happen as part of the scanline,
+  // but in the hardware renderers we'll do it at the vertex. FF8 is a good test case here, once you go too far left
+  // in the first scene of Galbadia Missile Base, the screen will flicker.
+  ALWAYS_INLINE static s32 VertexPositionToVRAMCoordinate(s32 x) { return SignExtendN<11, s32>(x); }
+
   union VRAMPixel
   {
     u16 bits;