fix(textarea): add readonly attribute

[rapropos]

Addresses #2010.

[codecov]

Codecov Report

Merging #2011 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2011   +/-   ##
=======================================
  Coverage   90.64%   90.64%           
=======================================
  Files          97       97           
  Lines        4307     4307           
  Branches      579      579           
=======================================
  Hits         3904     3904           
  Misses        206      206           
  Partials      197      197

Impacted Files	Coverage Δ
packages/textfield/textarea.ts	100% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f7f5e33...9adaa9a. Read the comment docs.

[trimox]

LGTM! Thanks @rapropos 👍