extensionFromMime function
The default file extension for a given MIME type.
If mimeType has multiple associated extensions,
the returned string is one of those, chosen as the default
extension for that MIME type.
Returns null if mimeType is not a recognized and
supported MIME type.
Implementation
String? extensionFromMime(String mimeType) =>
_defaultMimeTypeMap[mimeType.toLowerCase()];