Add dart support (#919)

Co-authored-by: Alex Goodman <alex.goodman@anchore.com>

syft/pkg/dart_pub_metadata.go

@@ -0,0 +1,38 @@
+package pkg
+
+import (
+	"github.com/anchore/packageurl-go"
+	"github.com/anchore/syft/syft/linux"
+)
+
+type DartPubMetadata struct {
+	Name      string `mapstructure:"name" json:"name"`
+	Version   string `mapstructure:"version" json:"version"`
+	HostedURL string `mapstructure:"hosted_url" json:"hosted_url,omitempty"`
+	VcsURL    string `mapstructure:"vcs_url" json:"vcs_url,omitempty"`
+}
+
+func (m DartPubMetadata) PackageURL(_ *linux.Release) string {
+	var qualifiers packageurl.Qualifiers
+
+	if m.HostedURL != "" {
+		qualifiers = append(qualifiers, packageurl.Qualifier{
+			Key:   "hosted_url",
+			Value: m.HostedURL,
+		})
+	} else if m.VcsURL != "" { // Default to using Hosted if somehow both are provided
+		qualifiers = append(qualifiers, packageurl.Qualifier{
+			Key:   "vcs_url",
+			Value: m.VcsURL,
+		})
+	}
+
+	return packageurl.NewPackageURL(
+		packageurl.TypePub,
+		"",
+		m.Name,
+		m.Version,
+		qualifiers,
+		"",
+	).ToString()
+}