Make tooltip examples keyboard accessible

[jessiehuff]

What: Closes #3961
Simple update to tooltip examples to allow them to be keyboard accessible.

(Same as #3962 that got accidentally reverted.)

[patternfly-build]

PF4 preview: https://patternfly-react-pr-4157.surge.sh
A11y report: https://patternfly-react-pr-4157-coverage.surge.sh

[codecov-io]

Codecov Report

Merging #4157 into v4 will decrease coverage by 0.00%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##               v4    #4157      +/-   ##
==========================================
- Coverage   58.72%   58.71%   -0.01%     
==========================================
  Files         397      397              
  Lines        6008     6009       +1     
  Branches     2349     2350       +1     
==========================================
  Hits         3528     3528              
  Misses       2024     2024              
- Partials      456      457       +1     

Flag	Coverage Δ
#patternfly4	58.71% <50.00%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
...ckages/react-charts/src/components/Chart/Chart.tsx	51.51% <ø> (ø)
...eact-charts/src/components/ChartArea/ChartArea.tsx	100.00% <ø> (ø)
...eact-charts/src/components/ChartAxis/ChartAxis.tsx	87.50% <ø> (ø)
.../react-charts/src/components/ChartBar/ChartBar.tsx	100.00% <ø> (ø)
...-charts/src/components/ChartBullet/ChartBullet.tsx	58.42% <ø> (ø)
...ChartBullet/ChartBulletComparativeErrorMeasure.tsx	91.66% <ø> (ø)
...ents/ChartBullet/ChartBulletComparativeMeasure.tsx	61.53% <ø> (ø)
...artBullet/ChartBulletComparativeWarningMeasure.tsx	91.66% <ø> (ø)
...nents/ChartBullet/ChartBulletPrimaryDotMeasure.tsx	85.00% <ø> (ø)
...ChartBullet/ChartBulletPrimarySegmentedMeasure.tsx	64.28% <ø> (ø)
... and 12 more

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