[Android] Allow custom background drawable with a custom handler

[jsuarezruiz]

Description of Change

Allow custom background drawable with a custom handler on Android.

Entry	Editor	Time Picker	Date Picker

Note, as in the previous gif, we can add/remove the BackgroundColor or Background in addition to being able to customize the control with a custom handler, removing the background or setting a custom drawable.

Issues Fixed

Fixes #18720

[mattleibow]

I updated this PR to not need a flag but rather use a know type of drawable. If the drawable used in the background is a Maui*Drawable, then we know that we added it and can remove it. Otherwise, we don't do anything since the only alternative is that it was the user.

There is the case where the cross-platform view has a background set, then we keep existing behavior and always override the background with the one set in the view. This means that if you have a custom handler that is going things AND set the background in XAML, the XAML will still win and override your custom background.

However, if you are trying to replace the background, make sure you are replacing the mapper instead of appending since you may be doubling the work needed to set the background (first maui code then your code):

builder.ConfigureMauiHandlers(handlers =>
{
#if ANDROID
    EntryHandler.Mapper.ReplaceMapping<IEntry, IEntryHandler>("Background", (handler, view) =>
    {
        var platformView = handler.PlatformView;

        // Android will reset the padding when setting a Background drawable, so we need to reapply the padding after
        var padLeft = platformView.PaddingLeft;
        var padTop = platformView.PaddingTop;
        var padRight = platformView.PaddingRight;
        var padBottom = platformView.PaddingBottom;

        // Set the custom background
        var gd = new Android.Graphics.Drawables.GradientDrawable();
        gd.SetCornerRadius(3);
        gd.SetStroke(1, Android.Graphics.Color.Red);
        gd.SetColor(Android.Graphics.Color.Pink);
        platformView.Background = gd;

        // Apply previous padding
        platformView.SetPadding(padLeft, padTop, padRight, padBottom);
    });
#endif
});

[mattleibow]

/azp run MAUI-UITests-public

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