Test extension host restart participation

[bpasero]

Refs: #180514

• anyOS @amunger
• anyOS @sandy081

Complexity: 2

Create Issue

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We have a few cases where we explicitly restart the extension host (for example when changing a profile) in the same window without window reload. This milestone we added a participation model to perform some work when this happens that is required to still finish on the old extension host before the new one starts.

Testing

• have dirty notebooks and dirty custom editors (for example LunaPaint)
• trigger an extension host restart, for example by
  • changing profiles
  • adding a folder to a single folder workspace (and thus entering an untitled workspace)
• verify that the dirty notebooks and dirty custom editors have successfully saved and there is no dataloss