Make iOS scanner view appear as Android does

[dustin-graham]

With a scan window and a scan line. barcodes should only scan if they intersect with the scan line.

[dustin-graham]

PR: https://github.com/apptreesoftware/flutter_barcode_reader/pull/34

@matthewtsmith ^

[matthewtsmith]

@dustin-graham I had to remove the scanLine change you added in #34 .

https://github.com/apptreesoftware/flutter_barcode_reader/pull/42

It was causing QR codes not to read.

[dustin-graham]

@matthewtsmith I'll look back at it again to see if I can make it work. In my case I really need the scan line for precision in my app's scenarios.