Copy textwriter.py from botocore project

[jwhitlock]

Re issue #4719, botocore/docs/bcdoc/textwriter.py is not used by botocore, and may be deleted in botocore to remove the docutils dependency. This PR imports the code into this project. There are no related tests to import.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov-io]

Codecov Report

Merging #4917 into develop will decrease coverage by 1.68%.
The diff coverage is 47.93%.

@@             Coverage Diff             @@
##           develop    #4917      +/-   ##
===========================================
- Coverage    93.94%   92.25%   -1.69%     
===========================================
  Files          189      190       +1     
  Lines        14524    15080     +556     
===========================================
+ Hits         13644    13912     +268     
- Misses         880     1168     +288

Impacted Files	Coverage Δ
awscli/help.py	96.48% <100%> (ø)	⬆️
awscli/textwriter.py	47.84% <47.84%> (ø)
awscli/customizations/ec2/bundleinstance.py	100% <0%> (+2.77%)	⬆️

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[kdaily]

Hi @jwhitlock, I think this will be taken care of by #5538. Thanks!