(Accessibility) Visualization/Lens - Images must have alternate text

[barlowm]

Steps to reproduce

1. From Kibana Home Page, use the side navigation bar to navigate to the "Visualize" page
2. Click the "Create visualization" button
3. Click the "Go to Lens" button, the "Stacked bar chart" image does not have alternate text.
   This is consistent across all the images in this location

Kibana Version:
7.8

OS:
Windows 7

Browser:
Chrome

Screen reader: [if relevant]
NVDA

Relevant WCAG Criteria: WCAG Criterion - Level A/AA/AAA
1.1.1 Non-text Content Level A

Relevant ARIA spec: WAI-ARIA Authoring Practices
N/A

[elasticmachine]

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

[wylieconlon]

Closed in 7.10. We are instead using svg role="img" aria-hidden="true" for these items.