Autocomplete: duplicates of existing terms are suggested (regression)

I think the changes requested in #24 can be reverted now that we don't support IE anymore. As mentioned in #32 we still need to address #4.

Confirmed the issue still exists on 10.1.x. The same solution should be able to apply, but we need tests and a reroll as well as removing the local cache.

Re-rolled #27 patch against 10.1.x.

Adding reroll for 10.1.x. Patch #27 throws the following error -
error: patch failed: core/misc/autocomplete.js:65
error: core/misc/autocomplete.js: patch does not apply

Still needs tests

Fix CCF errors.

My suggestion in #38 was a little misguided. What I meant is that we can indeed use includes instead of find.

Added changes according to #45

#46 doesn't fix the bug, and still needs tests.

Please guys, do not reroll or make changes to this patch if you're not going to properly test the functionality fixes the bug or read any other comments in the issue.

Here's a working fix with .includes. Still looking for existing JS tests for this widget but I don't think there are any.

I've created a MR with the changes of #79 to apply against D11 or D10.4. I've tested the patch locally and it works avoiding to display terms alreay applied when using an entity reference field with the widget "Autocomplete (tag style)"