[maps] replace euiPaletteX with @kbn/palette package

[nreese]

In preparation for the new Borealis theme, @elastic/kibana-visualizations change palettes in kibana. Previously palettes were defined in eui by static imports (i.e. euiPaletteColorBlind). But we now need a way to make these palettes theme-aware to toggle between the old Amsterdam palettes and the new Borealis palettes. In addition, we had multiple definitions of the same palettes.

First to make it easier @elastic/kibana-visualizations centralized the palette definitions in the new @kbn/palette package. This provides two methods for retrieving theme-aware palettes either getKbnPalettes or useKbnPalettes. You can read more about these changes in kibana#201015

Maps uses euiPaletteX calls directly and these should be transitioned to @kbn/palette equivalents. See eui#8112 for more details.

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)