Region flag upgrade & correct NTSC-U to NTSC-U/C

Replace references to NTSC-U with the correct NTSC-U/C and adds Canada in user-facing strings.
Replaces all region flags with revised SVGs.
Brings the US flag down to 3:2 to match Europe and Japan.
Adds a custom split US & Canada flag for the U/C region, also 3:2.
Generated PNGs and new HiDPI PNGs for region flags.
Flag PNGs were generated by downscaling using a Lanczos filter to a width of 36/72 pixels, then a 1px grey border added, then a 2/5px transparent border.

src/duckstation-qt/resources/icons/flag-jp.svg

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <svg xmlns="http://www.w3.org/2000/svg" width="900" height="600">
+<desc>Japanese flag</desc>
 <rect fill="#fff" height="600" width="900"/>
 <circle fill="#bc002d" cx="450" cy="300" r="180"/>
 </svg>