fix: correct main entry for relative path

[milaninfy]

npm-packlist gets normalized package-json when assessing files to include. when main is specified with relative file path it doesn't consider that entry when including files. Fixing main in normalization step

• check on changes condition
• sanity testing
• check npm pack command with empty files array in package.json
  • arborist node uses read-package-json-fast normalization functionality instead of package-json's normalization flow
• need to check for read-package-json-fast's normalization logic to replace it with package-json's normalization

Fixes: npm/cli#7799

[wraithgar]

A big refactor just happened here in anticipation of removing rpjf from arborist node. Note that it needs a completely different code path than normal, because it's in a class constructor. A new method was added to have parity with what happens now, which does NOT do bin lookups or underscore attribute stripping. A PR for arborist/node will be made once this package has its next release and we will finally be done with read-package-json-fast.

[milaninfy]

might need different code path changes after this replaces read-package-json-fast in cli