Review Mozilla 1916424: Support idle tasks in category manager JS invocations, to start using it from BrowserGlue

🔍 Bugzilla Audit

Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1916424

Moved the startup and shutdown init and uninit methods to BrowserComponents.manifest. Maybe we want to do the same with our components.

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