refactor: icon to icons for navbar

[pkdotson]

SUMMARY

This pr changes the triangle down icon to icons in the menu navbar.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

before

after

TESTING INSTRUCTIONS

Test out the navbar in different views Sqllab, listviews and homepage, and explore.

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 #15643 (b166910) into master (34542db) will increase coverage by 0.00%.
The diff coverage is 88.88%.

❗ Current head b166910 differs from pull request most recent head 94610c1. Consider uploading reports for the commit 94610c1 to get more accurate results

@@           Coverage Diff           @@
##           master   #15643   +/-   ##
=======================================
  Coverage   76.99%   76.99%           
=======================================
  Files         978      978           
  Lines       51486    51488    +2     
  Branches     6950     6951    +1     
=======================================
+ Hits        39642    39644    +2     
  Misses      11620    11620           
  Partials      224      224           

Flag	Coverage Δ
javascript	71.52% <88.88%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
superset-frontend/src/components/Menu/Menu.tsx	67.44% <66.66%> (+0.38%)	⬆️
superset-frontend/src/common/components/index.tsx	100.00% <100.00%> (ø)
...et-frontend/src/components/Menu/LanguagePicker.tsx	100.00% <100.00%> (ø)
...uperset-frontend/src/components/Menu/MenuRight.tsx	93.87% <100.00%> (ø)

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[pkdotson]

/testenv up

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@pkdotson Container image not yet published for this PR. Please try again when build is complete.

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@pkdotson Ephemeral environment creation failed. Please check the Actions logs for details.

[rusackas]

/testenv up

[github-actions]

@rusackas Ephemeral environment spinning up at http://34.211.173.177:8080. Credentials are admin/admin. Please allow several minutes for bootstrapping and startup.

[github-actions]

Ephemeral environment shutdown and build artifacts deleted.