fix(multi-select): add styles for filterable multiselect inputs

[emyarod]

Closes #2264

This PR adds styles for the input fields in the filterable multi select component

Changelog

New

• filterable multi select exposed in docs

Changed

• adjust left padding of filterable multi select input field. Note: this value will need to be adjusted by the consumer based on the number of selections in the component. i.e. the input field needs adjusted padding to account for the width of the number in <ListBox.Selection>

Testing / Reviewing

Ensure that the filterable multiselect is displaying properly

[netlify]

Deploy preview for the-carbon-components ready!

Built with commit 701c481

https://deploy-preview-2265--the-carbon-components.netlify.com

[emyarod]

if the new class is approved, the migration doc will need updates as well

[laurenmrice]

• There needs to be 8px padding from the left of the tag and to the right of the tag (before text)
  

[laurenmrice]

looks good to me 👍

[asudoh]

LGTM 👍 - Thanks @emyarod!