feat: run shrinkwrap during sf-prepack

[mdonnalley]

• Run npm shrinkwrap during sf-prepack
• Start managing plugin's files
• Add entires to .gitignore if they don't exist
  • if the CLEAN and CLEAN ALL segments exist, it will add the entries to the appropriate section (and remove them from anywhere else in the file)
  • if those segments don't exist, it will simply append the entries to the bottom of the file
• Change postpack script for plugins to sf-clean
• Remove shx devDep if it's not being used by any script

@W-14878497@

[shetzel]

QA looks good. I linked this to a plugin and ran yarn. Here are some screenshots. Everything is as expected.

I also linked it to a library and ran yarn. Everything that was changed was expected. Screenshots: