Add TrailingIcon property

[maurice0800]

🚀 Feature Requests

We should have the option to create a custom trailing icon.

Contextualize the feature

It would be useful to add a custom trailing icon for something like a password field. There could be a padlock icon at the end of the field which reveals the password when it is tapped.

Describe the feature

For this feature to work there are a few things required:

1. TrailingIconProperty
2. TrailingIconCommandProperty
3. TrailingIconCommandParameterProperty

All of this should be bindable to an ICommand too.

Platforms affected (mark all that apply)

• 📱 iOS
• 🤖 Android
• 🏁 WPF
• 🌎 UWP
• 🍎 MacOS
• 📺 tvOS
• 🐒 Xamarin.Forms