Ensure app is unmounted during unregisterApplication. Resolves #871

[internettrans]

See #871. This is technically a breaking change because it's conceivable someone could count on unregisterApplication to wait for applications to naturally unload.

[github-actions]

File size impact

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Error: Error while trying to generate a snapshot for 6.0.

Error: Command failed: npm install
npm WARN old lockfile 
npm WARN old lockfile The package-lock.json file was created with an old version of npm,
npm WARN old lockfile so supplemental metadata must be fetched from the registry.
npm WARN old lockfile 
npm WARN old lockfile This is a one-time fix-up, please be patient...
npm WARN old lockfile 
npm ERR! code EINVALIDPACKAGENAME
npm ERR! Invalid package name ".pnpm": name cannot start with a period

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/runner/.npm/_logs/2021-09-20T18_25_44_226Z-debug.log

    at ChildProcess.exithandler (node:child_process:397:12)
    at ChildProcess.emit (node:events:394:28)
    at maybeClose (node:internal/child_process:1064:16)
    at Process.ChildProcess._handle.onexit (node:internal/child_process:301:5)

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_{Generated by file size impact during file-size-impact#1254698161}

[TheMcMurder]

Seems like a reasonable approach to the problem.