I discovered that $wgShowEXIF when set to false, fully disables EXIF collection from files. (Including EXIF rotation information, used by the thumbnailing)

This doesn't really match the behavior as implied by its name, nor the behavior as described in https://www.mediawiki.org/wiki/Manual:$wgShowEXIF

• Add a new standard check for exif_ php availability
• Use that everywhere, instead of the config
• Remove the config variable as removed
• Add note to releasenotes