DataInspector: fix an attribute extraction bug for heatmaps & images

[Sagnac]

Description

Fixes #3101

If the colorrange attribute is left at default it returns MakieCore.Automatic; the method for get that was called at show_imagelike does not check for this type so the ensuing call to interpolated_getindex would fail.

The colorrange is now generically extracted and calculated_colors[].colorrange[] is preferred as it contains the actual range.

Type of change

• Bug fix (non-breaking change which fixes an issue)

[Sagnac]

I've updated the PR

[Sagnac]

Does everything look good now or are there other things I should change or add?

[SimonDanisch]

@ffreyer i think so right?
Maybe error instead of using (0, 1) since this can't be correct for DataInspector?

[ffreyer]

What's the state with heatmap and image now, after calculated_colors got added? Do those always include calculated_colors and does that always include a colorrange? If so it should just query that. (Since DataInspector relies on pick the first time these functions can get called is after the first render, if that matters.)

[SimonDanisch]

Yeah heatmap + image should always have calculated color, IF they map numbers to a color via colormap

[Sagnac]

Do you have a preference for the error message? I was going to go with colorrange not found, but I realize it's not very descriptive. Maybe something along the lines of
calculated_colors for the plot is missing or is not a proper color map. Please specify a colorrange.?

[SimonDanisch]

Since this should only be called for Heatmap/Image which always should have a colorrange in calculated_colors, I think this should be more of "this should not happen" internal kind of error.

[Sagnac]

How do things look now?

[SimonDanisch]

Thank you!! :)