graphics: synchronize option name for graphics/libheif

[tcberner]

Summary

• most ports use HEIF as option, do the same in
  • graphics/gimp-app and
  • graphics/kf5-kimageformats

[fluffy]

BTW, how about pass HEIF_DESC to Mk/bsd.options.desc.mk as standard name?

For gimp-app HEIF and JXL options good to set as default too, I forgot to do this with last gimp update :(

[tcberner]

In D35655#808539, @fluffy wrote:

BTW, how about pass HEIF_DESC to Mk/bsd.options.desc.mk as standard name?

For gimp-app HEIF and JXL options good to set as default too, I forgot to do this with last gimp update :(

Good idea, done in 4bed58cf4472f3065fd2132c06daadd1ab36bf5d

mfg Toibas