Add a new SimpleRenderer to handle simple cases.

[andydotxyz]

Description:

Easiest usage is to return NewSimpleRenderer(myObj) from CreateRenderer

Fixes #709

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.
• Public APIs match existing style.

[fpabl0]

I think this should be changed to:

func NewSimpleRenderer(object fyne.CanvasObject) *internalWidget.SimpleRenderer {
	return internalWidget.NewSimpleRenderer(object)
}

Otherwise, there is no way to use SimpleRenderer outside the Fyne repo.
Also I think that with this change every usage of SimpleRenderer in this package (widget) should use NewSimpleRenderer instead of internalWidget.NewSimpleRenderer (to keep consistency).

[andydotxyz]

Thanks, I missed the NewSimpleRenderer, and I will update the usages.
However the alias should remain, as we should not return internal objects from our public API.

[fpabl0]

Thanks, I missed the NewSimpleRenderer, and I will update the usages.

You're welcome :)

However the alias should remain, as we should not return internal objects from our public API.

Agree 👍

[fpabl0]

@andydotxyz I wonder if we should use fyne.WidgetRenderer directly instead of introducing a new type to the public API, in that way SimpleRenderer could be a private type simpleRenderer. By doing this we ensure that nobody tries to use the simple renderer as &SimpleRenderer{}. What do you think?

[andydotxyz]

Good question. Initially I was following the internal renderers etc and they have exposed methods (like SetObjects).
As this one doesn't we could return fyne.WidgetRenderer just now and revise it later if we need to add methods.

[fpabl0]

Looks good, just some comments :)

[fpabl0]

LGTM! :)