Add utility functions to draw detection results on android Canvas

[juliabeliaeva]

This PR includes:

1. Utility functions to draw detected objects on Canvas.
2. Function getPreviewImageBounds to calculate the correct coordinates and dimensions of the preview image to use for drawing.
3. Base class for View implementations which could be used for visualization.

Sample usage code:

class DetectorView(context: Context, attrs: AttributeSet) : DetectorViewBase<Result>(context, attrs) {
    private val objectPaint = ...
    private val textPaint = ...

    private var bounds: PreviewImageBounds? = null

    override fun onDetectionSet(detection: Result?) {
        bounds = detection?.let {
            getPreviewImageBounds(it.width, it.height, width, height, ScaleType.FILL_CENTER) 
            // important to use the same scale type as set in the target preview
        }
    }

    override fun Canvas.drawDetection(detection: Result) {
        val currentBounds = bounds ?: PreviewImageBounds(0f, 0f, width.toFloat(), height.toFloat())
        drawObject(detection.detection, currentBounds, objectPaint, textPaint)
    }
}

This view can be added along to the camera preview so it would draw its content on top of it:

<androidx.constraintlayout.widget.ConstraintLayout 
    //...
    <androidx.camera.view.PreviewView
            android:id="@+id/view_finder"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:scaleType="fillCenter"/>
    <DetectorView
            android:id="@+id/detector_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent"/>