Fix cn and ss flags losing stars and clamp svg render sizes

cn.svg and ss.svg defined their star polygons with coordinates around
plus/minus 5e5 compensated by tiny scale transforms. Qt drops shapes whose
device space bounds exceed its rasterizer coordinate limit, so both flags
silently lost their stars when rendered wider than roughly 76px. That
threshold was always exceeded because loadSvg with expandOnly renders at
the declared 640x480 native size before scaling down to the icon size.

Fold the scale transforms into the polygon coordinates so the geometry is
unchanged while bounds stay small at every render size.

Also cap expandOnly and usericon render canvases at four times the
requested size to bound memory use and keep pathological theme svgs away
from the rasterizer limit.

Took 8 minutes

Took 57 seconds


Took 3 minutes

cockatrice/resources/countries/cn.svg

@@ -52,8 +52,7 @@
      id="defs8">
     <polygon
        id="s"
-       points="-301930,415571 0,-513674 301930,415571 -488533,-158734 488533,-158734 "
-       transform="scale(1.94676e-6,1.94676e-6)"
+       points="-0.587785,0.809017 0,-1 0.587785,0.809017 -0.951057,-0.309017 0.951057,-0.309017 "
        style="fill:#ffde00" />
     <clipPath
        clipPathUnits="userSpaceOnUse"

cockatrice/resources/countries/ss.svg

@@ -16,6 +16,6 @@
   <rect id="rect10" height="2.88" width="12.8" y="4.278e-9" x="0"/>
   <rect id="rect12" height="2.88" width="12.8" y="3.36" x="0" fill="#da121a"/>
   <polygon id="polygon14" points="0 0 8.6603 5 0 10" fill="#0f47af" transform="scale(.96)"/>
-  <polygon id="polygon16" points="4.1557e5 -3.0193e5 -5.1367e5 0 4.1557e5 3.0193e5 -1.5873e5 -4.8853e5 -1.5873e5 4.8853e5" fill="#fcdd09" transform="matrix(.0000029902 0 0 .0000029902 2.7713 4.8)"/>
+  <polygon id="polygon16" points="4.01394 3.897169 1.23532 4.8 4.01394 5.702831 2.296666 3.3392 2.296666 6.2608" fill="#fcdd09"/>
  </g>
 </svg>