fix(autocomplete): show hover style on selected options (#4724)

Author: kara

src/lib/autocomplete/_autocomplete-theme.scss

@@ -9,7 +9,12 @@
     color: mat-color($foreground, text);
 
     .mat-option {
-      &.mat-selected:not(.mat-active) {
+      // Selected options in autocompletes should not be gray, but we
+      // only want to override the background for selected options if
+      // they are *not* in hover or focus state. This change has to be
+      // made here because base option styles are shared between the
+      // autocomplete and the select.
+      &.mat-selected:not(.mat-active):not(:hover) {
         background: mat-color($background, card);
         color: mat-color($foreground, text);
       }