Type fixes

[emmcb]

Some issues I found in types when migrating my typescript project to V3 beta:

• When we do not know the data point type, set unknown instead of guessing it is number. Putting number here prevent the user to cast to the actual data type, with a typescript error that number is not compatible and thus cannot be casted.
• As per the docs, we can assign new option object at runtime chart.options = {...}, so remove readonly modifier
• parsing options is not only a dataset option, it can also be given in the root chart options, so add it to IChartOptions
• ItooltipItem dataset property type should be IChartDataset
• ILinearScaleOptions should inherit from ICartesianScaleOptions (linear scale is a cartesian scale)
• tooltipFormat property were missing from time scale options

[emmcb]

Added one commit to fix axis property also missing on tooltip option.

[etimberg]

@sgratzl @kurkle thoughts on using unknown here? All of the other changes made sense to me, but for this one I'm not sure. It almost seems better to use a union type of the things we knowingly support number | string | Point

[kurkle]

number | string | Point is not sufficient through. We also support dates and arrays in float bars. The Point notation also supports numer/string/date/array of these for x/y or custom property. Commonly the data objects contain extra info for tooltips etc.
I'm not a ts user, but to me unknown here might make sense here.

[etimberg]

Good point on dates. Perhaps this is the least painful way to do it though users can accidentally pass bad data (e.g. the value is booleans and something in the chart will cast it to a number). For the custom properties part, that's probably where one would want to use a custom type.

[emmcb]

Most of my charts are time chart with custom {t, y} data points. While when creating chart I can use generics to give my custom DataPoint type, there are still some places like tooltip callback where we lose this and get back an abstract chart and dataset types. In these cases unknown is I think the best way to not make any guess and force the user to do the cast.

[xr0master]

Hello. Before it's merged, can I added a few issues with type?

1. IChartConfiguration doesn't have plugins, probably it should be plugins?: IPlugin[],
2. I think data also doesn't need the readonly flag, if we want to change all data.
3. In interface Chart the update method may have UpdateMode type instead of string.
4. What about creating units for a chart type instead of string? It may be like this:

type ChartTypePresets =
  | 'line'
  | 'bar'
  | 'radar'
  | 'doughnut'
  | 'pie'
  | 'polarArea'
  | 'bubble'
  | 'scatter';

type: ChartTypePresets | string; // string is for custom type

P.S. or shall I create own PR for these changes after this PR?

[etimberg]

@xr0master let's discuss those changes in their own PR