feat: Detect unused permissions in Snaps CLI

[Mrtenz]

This adds unused permission detection for handlers to the Snaps CLI. It will detect two cases:

• The Snap uses a certain permission, but does not export a handler for it.
• The Snap exports a handler, but does not request permission for it.

Unfortunately due to how it works, it did require some refactors to the CLI:

• The eval step in the build commands was removed in favour of the Webpack plugin. Having a separate step made it complicated to support things like watch mode, since that's handled by Webpack.
• Eval must run in order to detect unused permissions, so it's now run in the manifest command as well.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.13%. Comparing base (4acb5c3) to head (054ca79).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3335      +/-   ##
==========================================
+ Coverage   98.12%   98.13%   +0.01%     
==========================================
  Files         399      400       +1     
  Lines       10961    11027      +66     
  Branches     1725     1738      +13     
==========================================
+ Hits        10755    10821      +66     
  Misses        206      206              

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