Rework raw file http header logic (#20484)

- Always respect the user's configured mime type map
- Allow more types like image/pdf/video/audio to serve with correct content-type
- Shorten cache duration of raw files to 5 minutes, matching GitHub
- Don't set `content-disposition: attachment`, let the browser decide whether it wants to download or display a file directly
- Implement rfc5987 for filenames, remove previous hack. Confirmed it working in Safari.
- Make PDF attachment work in Safari by removing `sandbox` attribute.

This change will make a lot more file types open directly in browser now. Logic should generally be more readable than before with less `if` nesting and such.

Replaces: https://github.com/go-gitea/gitea/pull/20460
Replaces: https://github.com/go-gitea/gitea/pull/20455
Fixes: https://github.com/go-gitea/gitea/issues/20404

modules/typesniffer/typesniffer.go

@@ -70,6 +70,16 @@ func (ct SniffedType) IsRepresentableAsText() bool {
 	return ct.IsText() || ct.IsSvgImage()
 }
 
+// IsBrowsableType returns whether a non-text type can be displayed in a browser
+func (ct SniffedType) IsBrowsableBinaryType() bool {
+	return ct.IsImage() || ct.IsSvgImage() || ct.IsPDF() || ct.IsVideo() || ct.IsAudio()
+}
+
+// GetMimeType returns the mime type
+func (ct SniffedType) GetMimeType() string {
+	return strings.SplitN(ct.contentType, ";", 2)[0]
+}
+
 // DetectContentType extends http.DetectContentType with more content types. Defaults to text/unknown if input is empty.
 func DetectContentType(data []byte) SniffedType {
 	if len(data) == 0 {