media: Make Type comparable

So we can use it and output.Format as map key etc.

This commit also fixes the media.Type implementation so it does not need to mutate itself to handle different suffixes for the same MIME type, e.g. jpg vs. jpeg.

This means that there are no Suffix or FullSuffix on media.Type anymore.

Fixes #8317
Fixes #8324

parser/metadecoders/format.go

@@ -59,7 +59,7 @@ func FormatFromString(formatStr string) Format {
 // FormatFromMediaType gets the Format given a MIME type, empty string
 // if unknown.
 func FormatFromMediaType(m media.Type) Format {
-	for _, suffix := range m.Suffixes {
+	for _, suffix := range m.Suffixes() {
 		if f := FormatFromString(suffix); f != "" {
 			return f
 		}