[CM-1003] Add Elevation type

[karthikyml]

Introduction

Design specifies shadows differently than we do in code on iOS. They often refer to them as “elevations”.

Purpose

Elevation struct encapsulates data as per shadows in design software

Single operation:

func apply(layer: CAlayer, cornerRadius: CGFloat)

Sets shadow properties such as shadowOpacity, shadowColor, shadowOffset, shadowRadius

But shadowPath is only set in the case when useShadowPath is true. (Default is true)

Discussion

Because the implementation of spread requires a shadowPath, we will not be able to implement a shadow with a spread for a view whose shape we do not know. For example, shapes that are not rect or round rect.

Out of Scope

We might need to tweak the proposed spread algorithm i.e. add spread to corner radius as well.

📈 Coverage

Code

[mpospese]

@karthikyml This all looked really good but I made several adjustments once I started playing with it:

1. replace offset: CGSize with xOffset: CGFloat and yOffset: CGFloat to better match Figma / css
2. adjusted blur to shadowRadius conversion factor after experimentation in Figma + Xcode
3. adjusted shadowPath logic to include spread in adjusting the shadow's corner radius
4. clamped blur to be a minimum of 0
5. clamped opacity to be within 0...1
6. added an extent computed property that we can use to tell how far from the parent view a shadow spreads
7. moved Elevation from Components to Foundations folder. This is just a hierarchy of design elements. Shadows are primitives similar to colors and text styles.