Add aPNG downscaling

Goldenrequested to merge
Golden/SRB2:apng-downscale into next

Includes:

  • A consvar: apng_downscale (On/Off)
  • A menu option: Data Options > Screenshots > aPNG > Downscaling
  • A parity change so that GIF and aPNG downscaling menu options align

srb20132

Edited by Golden

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