Error State changes the IsEnabled state of MaterialTextField

## 🐛 Bug Report

On the XF.Material.Forms.UI.MaterialTextField, changing the HasError property sets IsEnabled to true.

### Expected behavior
The IsEnabled state should not be changed when HasError has changed

### Reproduction steps
When you change HasError to true then back to false, it sets IsEnabled to true. In the private method ChangeToNormalState it is has hard coded IsEnabled = True, this is clearly a bug as this will affect any existing binding to this property.

### Configuration

**Version:** 1.6.5

**Platform:**
- [ ] :iphone: iOS
- [ ] :robot: Android
- [ ] :checkered_flag: WPF
- [ ] :earth_americas: UWP
- [ ] :apple: MacOS
- [ ] :tv: tvOS
- [x ] :monkey: Xamarin.Forms