[Lens] Make Lens UI WCAG A compliant

[flash1293]

Lens UI should comply with WCAG A.

Tasks:

• Audit Lens and create list of violations
• Fix all violations
• Add automated tests [Lens] Add a11y tests #83594

WCAG A violations:

• Header structure (Accessibility) Fix page heading structure of Lens #58485
  • Missing H1 tag Visualization/Lens page is missing an H1 level heading #79933
• Query string input issue (Accessibility) Query string input - ARIA Role missing required child elements #79927 (comment)
• Missing keyboard navigation into dimension editor (Accessibility) Visualize/Lens - Missing Keyboard Navigation #79935
• Duplicate IDs in field list (Accessibility) Visualization/Lens - Duplicate IDs #79931
• Missing alt text on images (Accessibility) Visualization/Lens - Images must have alternate text #79923
• Focus is lost when deleting a layer [Lens] (Accessibility) Focus is lost when deleting a layer #83595
• Cannot change index patterns using a keyboard [Lens] (Accessibility) Cannot change index patterns using a keyboard  #83598
• Records field is a button but does nothing with a keyboard [Lens] (Accessibility) Records field is a button but does nothing with a keyboard #83600
• Suggestions have no focus state and no accessible name [Lens] (Accessibility) Suggestions have no focus state and no accessible name #83602
• No way to recreate "drag to workspace" with keyboard [Lens] (Accessibility) No way to recreate "drag to workspace" with keyboard #83730
• Field search gives no indication to screen readers that anything is happening [Lens] (Accessibility) Field search gives no indication to screen readers that anything is happening #83744

Best practice:

• Focus mistakenly stops on righthand form [Lens] (Accessibility) Focus mistakenly stops on righthand form #83591
• Improve landmarks [Lens] (Accessibility) Improve landmarks in Lens  #83597
• Improve screen reader announcement of the layer settings button [Lens] (Accessibility) Improve screen reader announcement of the layer settings button #83599
• Small HTML improvements for better screen reader support [Lens](Accessibility) Small HTML improvements for better screen reader support #83872
• convert select a function buttons to radio group for better screen reader support [Lens](Accessibility) convert select a function buttons to radio group for better screen reader support #84664

[elasticmachine]

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

[flash1293]

Everything from this list on the Lens side is done, let's close the issue and treat all upcoming a11y issues as bugs