(Accessibility) a11y violation : Ensures every id attribute value is unique - seen when you edit the dashboard .

[rashmivkulkarni]

[Please add a WCAG level label: WCAG A/AA/AAA]

Steps to reproduce

1. Login as an user and load sample data
2. Open dashboard panels

3. While running the dashboard panel a11y test - found this violation :

[duplicate-id]:  info Current URL is: http://localhost:5620/app/dashboards#/view/7adfa750-4c81-11e8-b3d7-01146121b73d?_g=(filters:!(),refreshInterval:(pause:!f,value:900000),time:(from:now-24h,to:now))&_a=(description:%27Analyze%20mock%20flight%20data%20for%20ES-Air,%20Logstash%20Airways,%20Kibana%20Airlines%20and%20JetBeats%27,filters:!(),fullScreenMode:!f,options:(hidePanelTitles:!f,useMargins:!t),query:(language:kuery,query:%27%27),timeRestore:!t,title:%27%5BFlights%5D%20Global%20Flight%20Dashboard%27,viewMode:view)
     │ info Saving page source to: /Users/rashmikulkarni/Documents/kibana/x-pack/test/functional/failure_debug/html/Dashboard Panel dashboard panel open .html
     └- ✖ fail: Dashboard Panel dashboard panel open 
     │      Error: a11y report:
     │ 
     │ VIOLATION
     │   [duplicate-id]: Ensures every id attribute value is unique
     │     Help: https://dequeuniversity.com/rules/axe/3.5/duplicate-id?application=axeAPI
     │     Elements:
     │       - div[data-layerid="x8xpo"]
     │       - div[data-layerid="x8xpo"] > .mapTocEntry-visible > .mapLayTocActions.euiPopover--anchorLeftUp.euiPopover--withTitle > .mapLayTocActions__popoverAnchor.euiPopover__anchor > .mapLayTocActions__tooltipAnchor.euiToolTipAnchor > .mapTocEntry__layerName.eui-textLeft.euiButtonEmpty--text > .euiButtonEmpty__content.euiButtonContent > .euiButtonEmpty__text > .mapTocEntry__layerNameIcon > .mapFillableCircle.euiIcon--medium[viewBox="\30 \ 0\ 16\ 16"] > defs > path
     │       - div[data-layerid="x8xpo"] > .mapTocEntry-visible > .mapLayTocActions.euiPopover--anchorLeftUp.euiPopover--withTitle > .mapLayTocActions__popoverAnchor.euiPopover__anchor > .mapLayTocActions__tooltipAnchor.euiToolTipAnchor > .mapTocEntry__layerName.eui-textLeft.euiButtonEmpty--text > .euiButtonEmpty__content.euiButtonContent > .euiButtonEmpty__text > .mapTocEntry__layerNameIcon > .mapFillableCircle.euiIcon--medium[viewBox="\30 \ 0\ 16\ 16"] > g > ellipse
     │       - div[data-layerid="y4jsz"]
     │       - div[data-layerid="jzppx"]
     │       - div[data-layerid="\30 hmz5"]
     │ 

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)