#8769: introduce PackageInstance type to disambiguate from Metadata definition/instance use cases

[twschiller]

What does this PR do?

• Closes Use separate type names for Metadata use cases #8769
• Stacked on #8761: update internal/external naming from brick to package in the Workshop #8762. Review/merge that PR first

Discussion

• The Metadata and PackageInstance types are currently equivalent, so this change only provides readability improvements, but no enforcement

Future Work

• Rename brickModalNoTags and related code to use package terminology

For more information on our expectations for the PR process, see the
code review principles doc

[github-actions]

Playwright test results

 82 passed
 2 flaky
 2 skipped

Details

 Open report ↗︎
 86 tests across 30 suites
 13 minutes, 12 seconds
 08a079f

Flaky tests

chrome › tests/regressions/welcomeStarterBricks.spec.ts › #8740: can view the starter mods on the pixiebrix.com/welcome page
edge › tests/regressions/welcomeStarterBricks.spec.ts › #8740: can view the starter mods on the pixiebrix.com/welcome page

Skipped tests

chrome › tests/runtime/googleSheetsIntegration.spec.ts › can activate a google spreadsheet mod with config options
edge › tests/runtime/googleSheetsIntegration.spec.ts › can activate a google spreadsheet mod with config options

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 61.11111% with 7 lines in your changes missing coverage. Please review.

Project coverage is 74.24%. Comparing base (8318d74) to head (08a079f).
Report is 26 commits behind head on main.

Files	Patch %	Lines
...es/packageEditor/referenceTab/PackageReference.tsx	0.00%	3 Missing ⚠️
src/components/brickModalNoTags/BrickModal.tsx	0.00%	2 Missing ⚠️
src/components/brickModalNoTags/BrickResult.tsx	0.00%	1 Missing ⚠️
src/components/brickModalNoTags/QuickAdd.tsx	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8770   +/-   ##
=======================================
  Coverage   74.24%   74.24%           
=======================================
  Files        1332     1332           
  Lines       40817    40857   +40     
  Branches     7634     7640    +6     
=======================================
+ Hits        30306    30336   +30     
- Misses      10511    10521   +10     

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