Fix search bottom bar UI

[kmcginnes]

Issue #, if available: #261

Description of changes:

• Arrange layout using flex and gaps
• Use Button component instead of IconButton

Before

NOTE: The "Clear Selected" button is currently in the hover state in this screenshot, showing the incorrect behavior it has today compared to other buttons.

After

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 17 lines in your changes are missing coverage. Please review.

Project coverage is 10.95%. Comparing base (33e7e2f) to head (ca31840).

Files	Patch %	Lines
...plorer/src/modules/KeywordSearch/KeywordSearch.tsx	0.00%	17 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #260   +/-   ##
=======================================
  Coverage   10.94%   10.95%           
=======================================
  Files         409      409           
  Lines       30421    30417    -4     
  Branches      711      711           
=======================================
  Hits         3331     3331           
+ Misses      26757    26753    -4     
  Partials      333      333           

Flag	Coverage Δ
unittests	10.95% <0.00%> (+<0.01%)	⬆️

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[michaelnchin]

Tested on SageMaker Notebook, appearance and functionality all looks good. Thanks @kmcginnes !