[iOS] Support For Compound button

[guptaabhishe]

Support For compound button

This PR adds support for compound Button which is a new adaptive card element being proposed.

Spec for compound button

Property	Required	Type	Allowed values
type (inherited)	Yes	String. Must be CompoundButton
id (inherited)		String
requires (inherited)		Object
isVisible (inherited)		Boolean
separator (inherited)		Boolean
height (inherited)		String	Auto, Stretch
horizontalAlignment (inherited)		String	Left, Center, Right
Spacing (inherited)		String	None, Small, Default, Medium, Large, ExtraLarge
targetWidth (inherited)		String	VeryNarrow, Narrow, Standard, Wide
icon		IconInfo object (see next table)
badge		String	Markdown is not supported
title	Yes	String	Markdown is not supported
description		String	Markdown is not supported
select Action		Action object. All actions allowed except Action.ShowCard

Spec for iconInfo

Property	Required		Type	Allowed values
name	Yes		String	The name of the icon, as per the Fluent icon directory. Same as the name of the new Icon element.
size			String	xxSmall, xSmall, Small, Standard, Medium, Large, xLarge, xxLarge
style			String	Regular, Filled
color			String	default, dark, light, accent, good, warning, attention

Sample Card

[guptaabhishe]

@microsoft-github-policy-service agree company="Microsoft"

[guptaabhishe]

Looks good to me! Do you think some unit tests can be added for this feature?

Added some unit tests