Implement support for method calls in the `content` tool.

  $ content call
    --uri content://com.example
    --method methodname
    [--arg optional_string_arg]
    [--extra name:s:foo --extra value:i:0]

The URI is just used to resolve the provider. --extra has
the same syntax as --bind.

Change-Id: I98cb89f0174a00e7c29ca0d8c8d809d453de3623