tv-casting-app CLI input should not block main thread

[sharadb-amazon]

Problem

See #8824 main.cpp. The PR sets stdin to O_NONBLOCK. The scanf() call blocks the main thread (though it does not block the event loop).

Proposed Solution

Leverage shell-common (src/lib/shell/MainLoopDefault.cpp) to accept user input.

[stale]

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[stale]

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