Use upper and lower invariant for ToUpperCamelCase

[Mushymato]

Log: https://smapi.io/log/57b9b049c3a649569ae83914f5d4aa61

Failed to update node:

  <grid item-layout="length: 192" horizontal-item-alignment="middle"/>

StardewUI.Framework.Descriptors.DescriptorException: Type Grid does not have a property named 'İtemLayout'.
   at StardewUI.Framework.Descriptors.IObjectDescriptor.GetProperty(String name) in D:\Repo\StardewUI\Framework\Descriptors\IObjectDescriptor.cs:line 73
   at StardewUI.Framework.Binding.AttributeBindingFactory.TryCreateBinding(IViewDescriptor viewDescriptor, IAttribute attribute, BindingContext context, IResolutionScope resolutionScope) in D:\Repo\StardewUI\Framework\Binding\AttributeBindingFactory.cs:line 169
   at StardewUI.Framework.Binding.ReflectionViewBinder.<>c__DisplayClass3_0.<Bind>b__1(IAttribute attribute) in D:\Repo\StardewUI\Framework\Binding\ReflectionViewBinder.cs:line 30

Issue where item-layout became İtemLayout after camel casing.

Test build:
StardewUI 0.6.1.zip