PWA template (#18878)

* Add service worker

* Add manifest

* Bring back BaselineTest.cs

* Add baselines for blazorwasm templates

* Add publishing test for PWA template

* Baseline fixes

* Fix baseline test logic to allow for multi-project outputs

* Remove non-blazorwasm baselines, since this branch now only covers blazorwasm

* Add test for PWA publish output

* Beginning generation of assets manifest

* Generate assets manifest including blazor outputs

* Tweaks

* Write assets manifest in JSON form

* Publish service worker

* Better API

* More resilience

* Better API again

* Make ComputeBlazorAssetsManifestItems public as people will need to customize the list

* Exclude service worker files from assets manifest

* Use web standard format for hash

* Update project template

* In assets manifest, only include items being published

* Renames

* Compute default assets manifest version by combining hashes

* Emit sw manifest in .js form

* Update service worker in project

* Actually isolate browser instances when requested during E2E tests

* E2E test for published PWA operating offline

* Fix SWAM path in template

* Clarify targets