Develop PlotlyView - A generally reusable UIView for displaying Figures

[vojtamolda]

To make the library easier to use on Apple devices (i.e. iOS/iPadOS/macOS) it would be nice to develop a generally reusable UIView. Such UI component can then be used as a "LEGO block" that displays a chart within a larger app.

PlotlyView should be a subclass of WKWebView and expose it's model as a settable property of type Plotly.Figure. Simply setting the figure object should be everything one needs to display a chart.

Here's an example use:

import Plotly

let trace = Scatter(
    x: [1, 2, 3],
    y: [3, 4, 5]
)

var view = PlotlyView()
view.figure = Figure(data: [trace])

---

Developing PlotlyView helps a great deal with building the standalone viewer app per #7. For more details about the motivation and general background check out the discussion in #11.

[vojtamolda]

Here's a few pieces of code that may be helpful to read before getting started:

• Extension that uses WebView to display debugging visualization:
  Plotly/Extensions/Playground.swift
• Xcode playground for macOS that shows a plot in a WebView:
  Examples/Playgrounds/

[vojtamolda]

Here's a suggestted task list:

• 0. Make sure the project can be built for iOS/iPadOS.

• 1. Convert the playground example to use UIKit instead of AppKit (i.e. iOS/iPadOS instead of macOS). This is needed because we eventually want to use Catalyst to support macOS.

• 2. Start iterating on the design of PlotlyView from the code converted in 1. The Xcode Playgrounds may be a good place to do it.

• 3. Once the design of PlotlyView makes sense from a user's perspective, try to build a sample iOS/iPadOS application that shows a very simple plot. This may eventually end up in the Examples/ folder as a demo.

• 4. Attempt Create a standalone chart viewer app #7 to see how the design works in a larger project. The point of doing this is to reveal missing features and delegate callbacks.