[elastic-charts] Amsterdam theme support

[nickofthyme]

Currently, @elastic/charts uses many styles from eui but not yet the Amsterdam theme. This causes issues within the chart legend when :focus states styles are overridden at a root level, such as here....

kibana/src/core/public/styles/_base.scss

Lines 8 to 17 in 2193111

	// We apply brute force focus states to anything not coming from Eui
	// which has focus states designed at the component level.
	// You can also use "kbn-resetFocusState" to not apply the default focus
	// state. This is useful when you've already hand crafted your own
	// focus states in Kibana.
	:focus {
	&:not([class^='eui']):not(.kbn-resetFocusState) {
	@include euiFocusRing;
	}
	}

The fix is for elastic-charts to adopt the Amsterdam theme natively such that the style overrides has no to minimal effect.

[elasticmachine]

Pinging @elastic/datavis (Feature:ElasticCharts)

[stratoula]

@nickofthyme can we close this?

[elasticmachine]

Pinging @elastic/kibana-visualizations @elastic/kibana-visualizations-external (Team:Visualizations)