Add more Sample Option Attributes

[michael-hawker]

Related #149

Realized as we've been building more samples, that just having bool and multi-choice as our options is a bit limiting, so wanted to list out some other simple scenarios for ToolkitSample*OptionAttributes we may want in the future:

Name	Parameters	Description
ToolkitSampleCommandOptionAttribute	label + nameof(SomeMethodOnSampleClass)	Creates a Button with label content which will execute the command when clicked
ToolkitSampleTextOptionAttribute	title (as normal) + placeholder	Creates a TextBox with placeholder text, allows user to type freeform text
ToolkitSampleSliderOptionAttribute	min + max + step + initial	Creates a Slider

We may also want a flag for MultiChoice to change whether it's radio buttons or a combobox?

We can always refer to our existing sample methods for ideas.

[michael-hawker]

Also found an issue trying to TwoWay bind to a ToolkitSampleBoolOption value. Uno throws an error in its XAML source generator that it can't find the property.

See a34ec37

[Arlodotexe]

Also found an issue trying to TwoWay bind to a ToolkitSampleBoolOption value. Uno throws an error in its XAML source generator that it can't find the property.

Thanks, we'll get that fixed up when we move focus back to Labs again.