feat: separate out blockMain

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🚀 Feature: Allow not putting a main in package.json #2048
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Separates out the concept of a "main" file to into its own blockMain. blockTSup now takes in runInCI as a general list of steps after pnpm build.

🎁

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.81%. Comparing base (47acb5f) to head (511d29b).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2050   +/-   ##
=======================================
  Coverage   99.81%   99.81%           
=======================================
  Files         119      120    +1     
  Lines        4921     4952   +31     
  Branches      307      308    +1     
=======================================
+ Hits         4912     4943   +31     
  Misses          9        9           

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[github-actions]

🎉 This is included in version v2.16.0 🎉

The release is available on:

• GitHub releases
• npm package (@latest dist-tag)

Cheers! 📦🚀