dev-cmd/generate-cask-api: start generating cask internal JSON v3

[apainintheneck]

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Part of #16410

This adds a new file to the output of brew generate-cask-api which represents the new internal JSON v3 file. It involves removing a bunch of unneeded hash keys while removing blank ones as well.

I've made some slight changes to the cask loader as well but more might be necessary before this starts loading things correctly. The full loader code will be added in a separate PR.

Changes

Skippable hash fields

• appcast
  • This is disabled right now and no longer used in the core cask tap.
• deprecated
  • Not used
• disabled
  • Not used
• full_token
  • Not used
• tap
  • Will be included in tap api hash
• tap_git_head
  • Will be included in tap api hash
• ruby_source_checksum
  • Replaced by ruby_source_sha256 to match formula API hash

Nilable hash fields

• languages
• container
• deprecation_date
• deprecation_reason
• disable_date
• disable_reason
• caveats
• depends_on
• conflicts_with
• url_specs

New hash fields

• caskfile_only
  • allows us to reduce the size of the artifacts array
• ruby_source_sha256
  • to match formula API hash

Updated cask loader

• to handle new ruby_source_sha256 field

Post Merge

• I'll open a PR to start signing this new file in formulae.brew.sh similar to this other PR for formulae: Start signing internal v3 json formulae.brew.sh#1069

[apainintheneck]

Before:

-rw-r--r--  1 kevinrobell  staff   6.5M Mar  2 15:29 cask.jws.json

After:

-rw-r--r--  1 kevinrobell  wheel   4.2M Mar  2 17:38 homebrew-cask.json

[MikeMcQuaid]

Looks good! A few non-blocking thoughts/comments.

[apainintheneck]

I'll merge this in tomorrow after I finish testing some things to make doubly sure that I'm not breaking current API JSON generation.

[MikeMcQuaid]

Looking good, thanks for making those changes ❤️

[apainintheneck]

Waiting on discussion in #16826 (comment)

Edit: It seems like that field isn't necessary.