Fix: unmarshal key values in Java, Go, and Conan metadata (#2603)

Previously, Syft represented several metadata fields as map[string]string,
however this representation erased ordering, so Syft now represents these values
as []KeyValue. Add custom unmarshaling so that JSON that was written by
older versions of Syft using the map[string]string representation can be parsed
into the new []KeyValue representation.

Signed-off-by: Will Murphy <will.murphy@anchore.com>

syft/pkg/java.go

@@ -1,6 +1,9 @@
 package pkg
 
 import (
+	"encoding/json"
+	"fmt"
+	"sort"
 	"strings"
 
 	"github.com/anchore/syft/internal"
@@ -70,6 +73,59 @@ type JavaManifest struct {
 	Sections []KeyValues `json:"sections,omitempty"`
 }
 
+type unmarshalJavaManifest JavaManifest
+
+type legacyJavaManifest struct {
+	Main          map[string]string            `json:"main"`
+	NamedSections map[string]map[string]string `json:"namedSections"`
+}
+
+func (m *JavaManifest) UnmarshalJSON(b []byte) error {
+	var either map[string]any
+	err := json.Unmarshal(b, &either)
+	if err != nil {
+		return fmt.Errorf("could not unmarshal java manifest: %w", err)
+	}
+	if _, ok := either["namedSections"]; ok {
+		var lm legacyJavaManifest
+		if err = json.Unmarshal(b, &lm); err != nil {
+			return fmt.Errorf("could not unmarshal java manifest: %w", err)
+		}
+		*m = lm.toNewManifest()
+		return nil
+	}
+	var jm unmarshalJavaManifest
+	err = json.Unmarshal(b, &jm)
+	if err != nil {
+		return fmt.Errorf("could not unmarshal java manifest: %w", err)
+	}
+	*m = JavaManifest(jm)
+	return nil
+}
+
+func (lm legacyJavaManifest) toNewManifest() JavaManifest {
+	var result JavaManifest
+	result.Main = keyValuesFromMap(lm.Main)
+	var sectionNames []string
+	for k := range lm.NamedSections {
+		sectionNames = append(sectionNames, k)
+	}
+	sort.Strings(sectionNames)
+	var sections []KeyValues
+	for _, name := range sectionNames {
+		section := KeyValues{
+			KeyValue{
+				Key:   "Name",
+				Value: name,
+			},
+		}
+		section = append(section, keyValuesFromMap(lm.NamedSections[name])...)
+		sections = append(sections, section)
+	}
+	result.Sections = sections
+	return result
+}
+
 func (m JavaManifest) Section(name string) KeyValues {
 	for _, section := range m.Sections {
 		if sectionName, ok := section.Get("Name"); ok && sectionName == name {