fix(datalist): use opacity instead display to hide caret icon (#855)

## PR Checklist

Please check if your PR fulfills the following requirements:

- [ ] Tests for the changes have been added (for bug fixes / features)
- [ ] Docs have been added / updated (for bug fixes / features)
- [ ] If applicable, have a visual design approval

## PR Type

What kind of change does this PR introduce?

<!-- Please check the one that applies to this PR using "x". -->

- [X] Bugfix
- [ ] Feature
- [ ] Code style update (formatting, local variables)
- [ ] Refactoring (no functional changes, no api changes)
- [ ] Build related changes
- [ ] CI related changes
- [ ] Documentation content changes
- [ ] Other... Please describe:

## What is the current behavior?

Currently the picker indicator of datalist is hidden with display: none
but that's not working for all browsers.

Issue Number: N/A

## What is the new behavior?

Now opacity: 0 is used which works for picker indicator on all
browsers..

## Does this PR introduce a breaking change?

- [ ] Yes
- [X] No

<!-- If this PR contains a breaking change, please describe the impact
and migration path for existing applications below. -->

## Other information

projects/angular/src/forms/styles/_datalist.clarity.scss

@@ -10,7 +10,7 @@
 
 input[clrDatalistInput] {
   &::-webkit-calendar-picker-indicator {
-    display: none;
+    opacity: 0;
     cursor: text;
   }
 }