chore(TextArea): Convert TextArea to typescript

[tlabaj]

#1953

What:

Additional issues:

[patternfly-build]

PatternFly-React preview: https://2168-pr-patternfly-react-patternfly.surge.sh

[codecov-io]

Codecov Report

Merging #2168 into master will decrease coverage by 0.18%.
The diff coverage is 93.75%.

@@            Coverage Diff             @@
##           master    #2168      +/-   ##
==========================================
- Coverage   80.84%   80.66%   -0.19%     
==========================================
  Files         651      661      +10     
  Lines        8260     8327      +67     
  Branches      628      631       +3     
==========================================
+ Hits         6678     6717      +39     
- Misses       1282     1309      +27     
- Partials      300      301       +1

Flag	Coverage Δ
#patternfly3	85.22% <ø> (ø)	⬆️
#patternfly4	76.18% <93.75%> (-0.3%)	⬇️
#patternflymisc	95.68% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
...nfly-4/react-core/src/components/TextArea/index.ts	100% <100%> (ø)
...-4/react-core/src/components/TextArea/TextArea.tsx	93.33% <93.33%> (ø)
...atternfly-4/react-core/src/components/Page/Page.js	47.61% <0%> (-6.55%)	⬇️
...s/patternfly-4/react-core/src/layouts/Grid/Grid.js	93.33% <0%> (-1.12%)	⬇️
...ct-core/src/components/Pagination/OptionsToggle.js	83.33% <0%> (ø)	⬆️
...y-3/patternfly-react/src/components/Label/Label.js	100% <0%> (ø)	⬆️
...y-4/react-core/src/components/Progress/Progress.js	100% <0%> (ø)	⬆️
...4/react-core/src/components/Accordion/Accordion.js	100% <0%> (ø)	⬆️
...fly-3/patternfly-react/src/components/Form/Form.js	100% <0%> (ø)	⬆️
...y-3/patternfly-react/src/components/Alert/Alert.js	100% <0%> (ø)	⬆️
... and 29 more

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[dlabaj]

LGTM