Fix autoResize functionality

[ThomasBower]

Resolves #60, resolves #141

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Personally, I believe that the current autoResize implementation is incorrect. Currently, the resize() function on the echarts instance is only called if the window resize event is fired. If I set autoResize to true, I would expect the graph to resize whenever its container size is changed, not only when the window is resized.

Moreover, even when the window is resized, there is no guarantee that the chart container needs to be resized, causing needless calls to the resize function. What we should actually be doing is checking when the surrounding container is resized as this is a much more reliable indicator that we need to resize and redraw the graph.

@xieziyu has previously justified this behaviour in #60 by saying (roughly translated) "the size change of the container is usually caused by some human factor. That is to say, the code should know when the container change will occur.", but I don't think it is reasonable to expect every other component on the page which could potentially cause the graph container to change size to directly call the resize event on the echarts instance. This behaviour should be handled in the chart component directly.

Please let me know what you think, as I think the behaviour shown here is a big improvement over the current implementation.

[xieziyu]

Appreciate for your work. I agree with you about the expected behaviour.
But the ResizeObserver spec is still in the ED status, and not supported by some browers. Maybe a polyfill should be imported when needed.

[ThomasBower]

@xieziyu Good point and thanks for the feedback. It has ~86% coverage but some big gaps on some mobile browsers and Internet Explorer. I've imported the polyfill we can use.

[ThomasBower]

@xieziyu Did you get a chance to have a look at the changes? Thanks.