Improve SVG bar chart accessibility

[plouc]

• Add support for various aria attributes to the SVG bar chart
• Add support for various aria attributes to the core SVG wrapper
• Mark SVG defs as hidden for screen readers
• Make bar items focusable and trigger tooltip when focused
• Use a single React hook to handle both bar SVG and Canvas implementations
• Improve the accessibility of the website component tabs used to switch between chart/code/data
• Allow markdown for components' help content
• Do not use target="_blank" for links in markdown as it's generally considered not to be the best practice
• Update caniuse-lite

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[bradlocking]

Hey Raphaël - Thanks for adding accessibility support to the bar chart component! We're currently working with a few other charts (Pie, Sunburst) and was wondering your thoughts on the complexity of getting broader accessibility support?