chore: Moves Dropdown to the components folder

[michael-s-molina]

SUMMARY

Moves Dropdown to the components folder.

This work is part of SIP-61

@rusackas @junlincc

TEST PLAN

1 - Execute all tests
2 - All tests should pass

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #14126 (2e4b7ae) into master (55bf72a) will not change coverage.
The diff coverage is n/a.

❗ Current head 2e4b7ae differs from pull request most recent head 91363a0. Consider uploading reports for the commit 91363a0 to get more accurate results

@@           Coverage Diff           @@
##           master   #14126   +/-   ##
=======================================
  Coverage   77.04%   77.04%           
=======================================
  Files         946      946           
  Lines       47985    47985           
  Branches     5962     5962           
=======================================
  Hits        36970    36970           
  Misses      10814    10814           
  Partials      201      201           

Flag	Coverage Δ
javascript	72.15% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...rontend/src/SqlLab/components/TabbedSqlEditors.jsx	71.77% <ø> (ø)
...uperset-frontend/src/components/Dropdown/index.tsx	100.00% <ø> (ø)

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[rusackas]

LGTM, needs rebase.