Support for macOS

[eneko]

Add support for macOS (Big Sur at least)

Detailed Description

Currently, the source code only checks for watchOS, otherwise it assumes iOS is available.

At a minimum, support for MacOS Big Sur would be great. Support for Catalina might be harder to achieve, due to the lack of SF Symbols.

Context

Xcode 12 and SwiftUI for macOS make it really easy to build native macOS applications with SwiftUI

Possible Implementation

Use #if os(macOS) and @available(...) where needed.

[AppPear]

I happily accept PRs tho v2 is coming so it might worth to wait for it.

[ridmaur]

So will V2 support Mac OS Big Sur?

[gundrabur]

Please extend support to macOS 11 Big Sur! I would appreciate it!

[willtemperley]

Created a PR for macOS 11 support: https://github.com/AppPear/ChartView/pull/183