Add SPDX JSON format object (#584)

* remove existing spdxjson presenter + helpers

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* add new spdx22json format

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* add common sdpxhelpers (migrated)

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* use new common spdx helpers

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* wire up new spdx22json format object

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* remove lossless syft-specific property bags

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* remove spdxjson decoder and validator

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* add nil checks in spdx test helpers

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* remove empty default case

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* use explicit golden snapshot

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

internal/formats/spdx22json/test-fixtures/image-simple/Dockerfile

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+# Note: changes to this file will result in updating several test values. Consider making a new image fixture instead of editing this one.
+FROM scratch
+ADD file-1.txt /somefile-1.txt
+ADD file-2.txt /somefile-2.txt

internal/formats/spdx22json/test-fixtures/image-simple/file-1.txt

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+this file has contents

internal/formats/spdx22json/test-fixtures/image-simple/file-2.txt

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+file-2 contents!