fix(dropdown): Use custom CSS for no-caret option #1473

[jacobmllr95]

Description of PR:

This PR use custom CSS for the no-caret option on the <b-dropdown>component instead of removing the dropdown-toggle class from the toggle itself which can cause minor styling issues.

Closes #1473

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PR checklist:

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Enhancement to an existing feature
• ARIA accessibility
• Documentation update
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact:

The PR fulfills these requirements:

• It's submitted to the dev branch, not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fixes #xxxx[,#xxxx], where "xxxx" is the issue number)

If new features/enhancement/fixes are added or changed:

• Includes documentation updates
• New/updated tests are included and passing (if required)
• Existing test suites are passing
• The changes have not impacted the functionality of other components or directives
• ARIA Accessibility has been taken into consideration (does it affect screen reader users or keyboard only users?)

If adding a new feature, or changing the functionality of an existing feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

PR titles should following the Conventional Commits naming convention

[codecov]

Codecov Report

Merging #2136 into dev will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev    #2136   +/-   ##
=======================================
  Coverage   64.97%   64.97%           
=======================================
  Files         159      159           
  Lines        2958     2958           
  Branches      811      811           
=======================================
  Hits         1922     1922           
  Misses        749      749           
  Partials      287      287

Impacted Files	Coverage Δ
src/components/dropdown/dropdown.js	100% <ø> (ø)	⬆️

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