feat(dropdown): ♿ improve dropdown & autocomplete a11y

[ChildishGiant]

Dropdown and autocomplete now smoothly scrolls to elements selected with keyboard (Closes #12)

Here's a before and after:

Before

before.mp4

After

after.mp4

You can see I made it smooth scroll as the jumping about that was previously used can be a bit jarring.

Types of changes

Debatable since the current implementation was disabled for autocompletes because it didn't work.

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to change).

Checklist:

• I have read the CONTRIBUTING document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.