feat(core): add params to the postPackage hook

[malept]

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• I agree to follow the code of conduct that this project follows, as appropriate.
• The changes are appropriately documented (if applicable).
• The changes have sufficient test coverage (if applicable).
• The testsuite passes successfully on my local machine (if applicable).

Summarize your changes:

Adds the following parameters to postPackage:

• platform
• arch
• outputPaths (the result of await packager(...))
• spinner (the ora spinner, if defined)

Docs are at electron-forge/electron-forge-docs#12

Also, DRYs up the "update package.json" code.

Fixes #1630.

[codecov]

Codecov Report

Merging #1896 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1896   +/-   ##
=======================================
  Coverage   72.71%   72.71%           
=======================================
  Files          74       74           
  Lines        2210     2210           
  Branches      416      416           
=======================================
  Hits         1607     1607           
  Misses        443      443           
  Partials      160      160           

Impacted Files	Coverage Δ
packages/api/core/src/api/package.ts	74.73% <100.00%> (ø)

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