Add SPDX JSON format object

[wagoodman]

This is a follow up from #578

Continues on with the format pattern introduced in #550 with the spdx22json format. This is the same implementation that existed with the presenters, but does not support any additional capabilities (decoding or validation).

Additional work also done:

• migrated SPDX helpers under the formats package and split up the implementation into separate files

[github-actions]

Benchmark Test Results

Benchmark results from the latest changes vs base branch

name                                                   old time/op    new time/op    delta
ImagePackageCatalogers/ruby-gemspec-cataloger-2          1.52ms ± 7%    1.20ms ± 2%  -20.75%  (p=0.008 n=5+5)
ImagePackageCatalogers/python-package-cataloger-2        2.99ms ± 2%    2.43ms ± 2%  -18.67%  (p=0.008 n=5+5)
ImagePackageCatalogers/javascript-package-cataloger-2     894µs ± 2%     740µs ± 5%  -17.22%  (p=0.008 n=5+5)
ImagePackageCatalogers/dpkgdb-cataloger-2                 913µs ± 1%     755µs ± 1%  -17.33%  (p=0.016 n=5+4)
ImagePackageCatalogers/rpmdb-cataloger-2                  925µs ± 2%     840µs ±25%     ~     (p=0.151 n=5+5)
ImagePackageCatalogers/java-cataloger-2                  12.7ms ± 2%    11.1ms ± 6%  -13.18%  (p=0.008 n=5+5)
ImagePackageCatalogers/apkdb-cataloger-2                 1.22ms ± 1%    1.07ms ±14%     ~     (p=0.095 n=5+5)
ImagePackageCatalogers/go-module-binary-cataloger-2       752ns ± 3%     627ns ± 5%  -16.66%  (p=0.008 n=5+5)

name                                                   old alloc/op   new alloc/op   delta
ImagePackageCatalogers/ruby-gemspec-cataloger-2           227kB ± 0%     228kB ± 0%   +0.38%  (p=0.016 n=5+5)
ImagePackageCatalogers/python-package-cataloger-2         980kB ± 0%     980kB ± 0%   -0.04%  (p=0.016 n=5+5)
ImagePackageCatalogers/javascript-package-cataloger-2     192kB ± 0%     192kB ± 0%     ~     (p=0.222 n=5+5)
ImagePackageCatalogers/dpkgdb-cataloger-2                 211kB ± 0%     211kB ± 0%   -0.16%  (p=0.008 n=5+5)
ImagePackageCatalogers/rpmdb-cataloger-2                  217kB ± 0%     217kB ± 0%   -0.01%  (p=0.016 n=5+4)
ImagePackageCatalogers/java-cataloger-2                  3.12MB ± 0%    3.12MB ± 0%     ~     (p=0.056 n=5+5)
ImagePackageCatalogers/apkdb-cataloger-2                 1.26MB ± 0%    1.26MB ± 0%     ~     (p=0.095 n=5+5)
ImagePackageCatalogers/go-module-binary-cataloger-2        336B ± 0%      336B ± 0%     ~     (all equal)

name                                                   old allocs/op  new allocs/op  delta
ImagePackageCatalogers/ruby-gemspec-cataloger-2           5.46k ± 0%     5.46k ± 0%     ~     (all equal)
ImagePackageCatalogers/python-package-cataloger-2         18.1k ± 0%     18.1k ± 0%     ~     (p=0.540 n=5+5)
ImagePackageCatalogers/javascript-package-cataloger-2     4.80k ± 0%     4.80k ± 0%     ~     (all equal)
ImagePackageCatalogers/dpkgdb-cataloger-2                 5.53k ± 0%     5.53k ± 0%     ~     (all equal)
ImagePackageCatalogers/rpmdb-cataloger-2                  6.22k ± 0%     6.22k ± 0%     ~     (all equal)
ImagePackageCatalogers/java-cataloger-2                   51.5k ± 0%     51.5k ± 0%     ~     (p=0.413 n=5+5)
ImagePackageCatalogers/apkdb-cataloger-2                  5.49k ± 0%     5.49k ± 0%     ~     (p=0.881 n=5+5)
ImagePackageCatalogers/go-module-binary-cataloger-2        9.00 ± 0%      9.00 ± 0%     ~     (all equal)

[luhring]

Looks good! Treat all comments as "nit"!

(Another general "nit" for consideration would be to consider more use of vertical space to visually separate if/switch blocks, variable decls, and return statements.)