Deduplicate packages across multiple container image layers (#930)

internal/formats/spdx22json/test-fixtures/snapshot/TestSPDXJSONDirectoryEncoder.golden

@@ -3,18 +3,18 @@
  "name": "/some/path",
  "spdxVersion": "SPDX-2.2",
  "creationInfo": {
-  "created": "2021-12-20T19:12:47.869816Z",
+  "created": "2022-03-30T21:48:28.297464Z",
   "creators": [
    "Organization: Anchore, Inc",
    "Tool: syft-[not provided]"
   ],
-  "licenseListVersion": "3.15"
+  "licenseListVersion": "3.16"
  },
  "dataLicense": "CC0-1.0",
- "documentNamespace": "https://anchore.com/syft/dir/some/path-4b896ded-7852-4e31-b764-136b53bdf346",
+ "documentNamespace": "https://anchore.com/syft/dir/some/path-e188d59b-76f6-4c7f-a9f2-1ae7d0577781",
  "packages": [
   {
-   "SPDXID": "SPDXRef-1d97af55efe9512f",
+   "SPDXID": "SPDXRef-b85dbb4e6ece5082",
    "name": "package-1",
    "licenseConcluded": "MIT",
    "downloadLocation": "NOASSERTION",
@@ -36,7 +36,7 @@
    "versionInfo": "1.0.1"
   },
   {
-   "SPDXID": "SPDXRef-ad3d1c4abd84bf75",
+   "SPDXID": "SPDXRef-ceda99598967ae8d",
    "name": "package-2",
    "licenseConcluded": "NONE",
    "downloadLocation": "NOASSERTION",

internal/formats/spdx22json/test-fixtures/snapshot/TestSPDXJSONImageEncoder.golden

@@ -3,18 +3,18 @@
  "name": "user-image-input",
  "spdxVersion": "SPDX-2.2",
  "creationInfo": {
-  "created": "2021-12-20T19:13:07.647486Z",
+  "created": "2022-03-30T21:48:28.303986Z",
   "creators": [
    "Organization: Anchore, Inc",
    "Tool: syft-[not provided]"
   ],
-  "licenseListVersion": "3.15"
+  "licenseListVersion": "3.16"
  },
  "dataLicense": "CC0-1.0",
- "documentNamespace": "https://anchore.com/syft/image/user-image-input-174da656-1824-4bd3-8604-28919f8a65bc",
+ "documentNamespace": "https://anchore.com/syft/image/user-image-input-9e4f4190-c5ae-4e31-a852-d1ab71357516",
  "packages": [
   {
-   "SPDXID": "SPDXRef-d16127444133b5c1",
+   "SPDXID": "SPDXRef-2a46171f91c8d4bc",
    "name": "package-1",
    "licenseConcluded": "MIT",
    "downloadLocation": "NOASSERTION",
@@ -36,7 +36,7 @@
    "versionInfo": "1.0.1"
   },
   {
-   "SPDXID": "SPDXRef-24907357f3705420",
+   "SPDXID": "SPDXRef-ae77680e9b1d087e",
    "name": "package-2",
    "licenseConcluded": "NONE",
    "downloadLocation": "NOASSERTION",