Change provider to add no semicolon if one is already present

[MoritzKn]

Description of the Change

This PR will change the CSS autocomplete provider to add no semicolons after a CSS property if one is already present.

Example:

In this code

body {
  display: i;
}

Pressing ctrl-shift-space after display: i and choosing inline-block previously added another semicolon and therefore resulted in something like this:

body {
  display: inline-block;;
}

Alternate Designs

None

Benefits

Improves UX

Possible Drawbacks

Unknown

Applicable Issues

None

[winstliu]

Awesome! Looks like you have a lint error in the spec file, but that's it.

[MoritzKn]

Done. :) The lint error is fixed and the testes should pass CI too.

[winstliu]

Thanks!