fix(dropdown): add z-index for dropdown to not be overrided by modal

[daniloff200]

PR Checklist

closes #5144

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[codecov]

Codecov Report

Merging #5627 into development will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           development    #5627   +/-   ##
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  Coverage        52.52%   52.52%           
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  Files                3        3           
  Lines               99       99           
  Branches            17       17           
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  Hits                52       52           
  Misses              37       37           
  Partials            10       10

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[nigelsim]

I'm not sure 1040 is the correct value. From BS3 _variables.scss file the modal is at 1050.

$zindex-modal-background:  1040 !default;
$zindex-modal:             1050 !default;

Following this patch all of our dropdowns that are in modals started being put behind, where previously we had adjusted their z-index with CSS.