Remove separate packages for platform interface implementation

[natalieparellano]

Despite having advocated the current approach, I now regret it. Having to duplicate the entire previous platform when a new version is supported is not optimal. E.g. for platform 0.8, the only difference from 0.7 is that standardized sBOM is now supported, but we had to copy the entire directory and essentially do a find and replace to get everything to compile.

It would be awesome if we could still move logic into the platform package (e.g. here, this could be a SupportsSBOM field or method on Platform). But the proposed organization would allow us to do this at our own pace, and reduce a fair amount of duplication.

[natalieparellano]

Also makes the code slightly more efficient by having the Platform hold on to a *api.Version instead of a string.

[codecov]

Codecov Report

Merging #771 (9bec743) into main (071939d) will increase coverage by 3.17%.
The diff coverage is 44.69%.

❗ Current head 9bec743 differs from pull request most recent head 9d710f4. Consider uploading reports for the commit 9d710f4 to get more accurate results

@@            Coverage Diff             @@
##             main     #771      +/-   ##
==========================================
+ Coverage   62.32%   65.49%   +3.17%     
==========================================
  Files          59       55       -4     
  Lines        4100     4059      -41     
==========================================
+ Hits         2555     2658     +103     
+ Misses       1283     1121     -162     
- Partials      262      280      +18     

Flag	Coverage Δ
os_windows	65.49% <44.69%> (+3.17%)	⬆️

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