Add ZoomFactor property and implement platform zoom on iOS/Android/Windows

[darrabam]

Description

• Expose a bindable ZoomFactor property for CameraBarcodeReaderView to control camera zooming.
• Accept a float value [0 - 1] and maps it to each platform's supported zoom range.
• Ensure platform-specific behavior to avoid engaging digital zoom (iOS capped to optical max) and to use native linear zoom where appropriate.

Motivation

There are situations where by using zoom can considerably improve the detectability of Zxing.

Tests

It was manually tested on physical iOS/Android phones and Windows device with a camera.