fix(grapher): display line/bar chart icon depending on whether it's c…

[marcelgerber]

Alternative fix for #2769, closes #2769.

@sophiamersmann I checked, and all uses of isLineChartThatTurnedIntoDiscreteBar already guard against the situation where we're on the map tab, so ideally this shouldn't change the behavior (🤞🏻), and we don't need to introduce the isAuthoredAsLineChartThatTurnedIntoDiscreteBar property.

We can also get rid of the whole previousChartIcon logic, too.

One thing to watch out for, though, is that for time bounds in grapher there are two different types: There are "restricted" ones (i.e. natural numbers) and "unrestricted" ones (basically, natural numbers and ±Infinity).

minTime and maxTime are unrestriced, i.e. we can end up in situations like:

• minTime = -Infinity, maxTime = Infinity, resolved time span is 1980..1980
• minTime = -Infinity, maxTime = 1980, resolved time span is also 1980..1980
• ... you get the drill

For this reason, it's important to also "resolve" minTime and maxTime, and we do this using findClosestTime.

[sophiamersmann]

Works perfectly! Thanks so much for looking into this and coming up with a nice solution 🙌🏻