Expose ProvideTitle function publicly

[ovatsus]

In FSharpChart we could use ChartFormUtilities.ProvideTitle, but there's no equivalent in FSharp.Charting. This is needed when you want to use ChartControl directly to embed in an application instead of using it in FSI. The ShowChart function uses the ProvideTitle function to set the title of the form it creates, but if you need to show the chart any other way, there's currently no way to get at the title that would be generated