fix(text-field): Update helper text to use correct typography

[williamernest]

Add caption type to helper-text.

[codecov-io]

Codecov Report

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The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2618   +/-   ##
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  Coverage          ?   98.46%           
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  Files             ?       98           
  Lines             ?     4239           
  Branches          ?      538           
=========================================
  Hits              ?     4174           
  Misses            ?       65           
  Partials          ?        0

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