feature: annotations to be tied to the trace/point, not the chart-layout.

[RichardNeill]

Hovertext or Text are properties of a data point itself. I think it would be useful if the Annotations could be as well.

This would make it much easier to manipulate them, including:

• annotations would play nice with stacked and grouped bars.
• annotations can toggle on/off when a series is enabled/disabled by clicking in the legend.
• no need to specify x and y explicitly, thereby solving Annotations don't align with the bars if I use "category" axis type.  #5741 annotations aren't plotted properly on log axes #1258 and Implement lat/lon data-referenced annotations on geo and mapbox subplots #3834.

I think that a way to do this would be to have traces.annotations, in addition to layout.annotations.
Or, overload traces.textposition to have an "arrow" mode.

[gvwilson]

Hi - we are trying to tidy up the stale issues and PRs in Plotly's public repositories so that we can focus on things that are still important to our community. Since this one has been sitting for several years, I'm going to close it; if it is still a concern, please add a comment letting us know what recent version of our software you've checked it with so that I can reopen it and add it to our backlog. Thanks for your help - @gvwilson