fix(autocomplete): suggestions can be highlighted incorrectly

[Splaktar]

PR Checklist

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• The commit message follows our guidelines
• Tests for the changes have been added or this is not a bug fix / enhancement
• Docs have been added, updated, or were not required

PR Type

What kind of change does this PR introduce?

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

What is the current behavior?

The second time and beyond when a chips autocomplete dropdown panel is opened, there will be a background on some of the matches to indicate that they are selected, even when they are not selected. It's very confusing UX.

Using ng-class within md-virtual-repeat doesn't seem to be working
it was evaluating the following to true: -1 === 0, -1 === 1, etc.

Issue Number:
Fixes #10573.

What is the new behavior?

We no longer depend on ng-class here and use the #selected_option selector for styling.
This results in no bogus suggestions being highlighted as selected and only the hovered or selected items being highlighted.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

This could cause some issues for apps who are relying on the md-virtual-repeat li.selected class for styling their app. However, this is unlikely as this bug would have made styling based on that class unreliable.