Investigate Intents for launching external apps

We should investigate these items:

components/feature/app-links/src/main/java/mozilla/components/feature/app/links/AppLinksUseCases.kt
components/feature/contextmenu/src/main/java/mozilla/components/feature/contextmenu/ContextMenuCandidate.kt
components/feature/downloads/src/main/java/mozilla/components/feature/downloads/AbstractFetchDownloadService.kt
components/feature/downloads/src/main/java/mozilla/components/feature/downloads/DownloadsFeature.kt
components/feature/prompts/src/main/java/mozilla/components/feature/prompts/PromptContainer.kt
components/feature/prompts/src/main/java/mozilla/components/feature/prompts/file/FilePicker.kt
components/feature/pwa/src/main/java/mozilla/components/feature/pwa/WebAppInterceptor.kt
components/feature/app-links/src/main/java/mozilla/components/feature/app/links/AppLinksInterceptor.kt

And make sure we ask the user before launching, or block the intent if it's too dangerous (e.g. proxy bypass).