Fix plot_intensities for data on very large grids

[kbarros]

A very large grid passed to Makie.image or Makie.heatmap causes certain OpenGL backends to fail. Consequently, plot_intensities will not render certain data.

As discussed in MakieOrg/Makie.jl#4950, a workaround is to convert all uses of Makie.image to Makie.heatmap, and then wrap the grid data inside a Makie.Resampler object. That is implemented here.

Notes:

• Apart from this bug, Makie.image could be preferable over Makie.heatmap in other ways, e.g., data on a regular grid is faster to render. However, the two have some subtle rendering differences: axis ranges may change slightly, and heatmap does not interpolate between grid points like image seems to.
• No attempt is made to determine what grid sizes will cause rendering to fail for the given graphics hardware. We pick a conservative number, 2000 pixels along any axis, and create a Makie.Resampler if that threshold is reached.
• Caution is required around the ylims argument. With this PR, it is interpreted to apply after any energy units conversions are performed.
• Conversion in the opposite direction (heatmap to image) happened in Powder averaging of static intensities #374, which this PR partially undoes.