fix(docs): only load modules if package has entry point

[erickzhao]

Two small fixes:

• Better type for package.json in our utility code
• Doesn't attempt to run TypeDoc for a package if it doesn't have a main entry. Removes a warning message Warning: Could not determine the entry point for "/Users/erick.zhao/Developer/electron/forge/packages/api/cli/package.json". Package will be ignored.

[codecov]

Codecov Report

Merging #2981 (e669357) into main (a8b9dfc) will decrease coverage by 0.41%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #2981      +/-   ##
==========================================
- Coverage   73.78%   73.36%   -0.42%     
==========================================
  Files          66       66              
  Lines        2144     2144              
  Branches      423      423              
==========================================
- Hits         1582     1573       -9     
  Misses        359      359              
- Partials      203      212       +9     

Impacted Files	Coverage Δ
packages/maker/zip/src/MakerZIP.ts	90.90% <0.00%> (-9.10%)	⬇️
packages/api/core/src/api/make.ts	73.26% <0.00%> (-5.95%)	⬇️
packages/api/cli/src/util/check-system.ts	68.29% <0.00%> (-2.44%)	⬇️
packages/maker/appx/src/MakerAppX.ts	58.62% <0.00%> (-1.73%)	⬇️
packages/maker/deb/src/MakerDeb.ts	90.90% <0.00%> (ø)
packages/maker/rpm/src/MakerRpm.ts	90.90% <0.00%> (ø)

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