media: support application/manifest+json

The standard file extension for Web App Manifest files is
".webmanifest". This commit allows Hugo to recognize .webmanifest files
as "application/manifest+json" files and to minify them using its
JSON minifier.

The .webmanifest file extension is recommended in the w3c spec to
simplify media type registration:
https://www.w3.org/TR/appmanifest/#media-type-registration

Webhint docs are also relevant:
https://webhint.io/docs/user-guide/hints/hint-manifest-file-extension/

Closes #8624

media/mediaType.go

@@ -167,6 +167,7 @@ var (
 	JSXType        = newMediaType("text", "jsx", []string{"jsx"})
 
 	JSONType           = newMediaType("application", "json", []string{"json"})
+	WebAppManifestType = newMediaTypeWithMimeSuffix("application", "manifest", "json", []string{"webmanifest"})
 	RSSType            = newMediaTypeWithMimeSuffix("application", "rss", "xml", []string{"xml"})
 	XMLType            = newMediaType("application", "xml", []string{"xml"})
 	SVGType            = newMediaTypeWithMimeSuffix("image", "svg", "xml", []string{"svg"})
@@ -206,6 +207,7 @@ var DefaultTypes = Types{
 	TSXType,
 	JSXType,
 	JSONType,
+	WebAppManifestType,
 	RSSType,
 	XMLType,
 	SVGType,

minifiers/minifiers.go

@@ -78,7 +78,7 @@ func New(mediaTypes media.Types, outputFormats output.Formats, cfg config.Provid
 	}
 	if !conf.DisableJSON {
 		addMinifier(m, mediaTypes, "json", &conf.Tdewolff.JSON)
-		m.AddRegexp(regexp.MustCompile(`^(application|text)/(x-|ld\+)?json$`), &conf.Tdewolff.JSON)
+		m.AddRegexp(regexp.MustCompile(`^(application|text)/(x-|(ld|manifest)\+)?json$`), &conf.Tdewolff.JSON)
 	}
 	if !conf.DisableSVG {
 		addMinifier(m, mediaTypes, "svg", &conf.Tdewolff.SVG)

output/outputFormat.go

@@ -143,6 +143,14 @@ var (
 		Rel:         "alternate",
 	}
 
+	WebAppManifestFormat = Format{
+		Name:        "WebAppManifest",
+		MediaType:   media.WebAppManifestType,
+		BaseName:    "manifest",
+		IsPlainText: true,
+		Rel:         "manifest",
+	}
+
 	RobotsTxtFormat = Format{
 		Name:        "ROBOTS",
 		MediaType:   media.TextType,
@@ -176,6 +184,7 @@ var DefaultFormats = Formats{
 	CSVFormat,
 	HTMLFormat,
 	JSONFormat,
+	WebAppManifestFormat,
 	RobotsTxtFormat,
 	RSSFormat,
 	SitemapFormat,