The `TagEditor` component formerly did not take casing into account
in its formatting function for suggested tags. The match should be
case-insensitive in the formatter, as it is in the service that does
the filtering of tags.

This is fixed in two ways:

1. Make substring matching in the formatting function case-insensitive.
   Render the substring match according to the suggested tag's casing.
   Fixes this issue specifically.
2. Provide a fallback in the formatter for when the input text does not
   "seem" to match the suggested `item`. In these cases, just render the
   suggested tag as-is. This will prevent the formatter from spazzing
   out if its notion of matching differs from the tag-service's in
   any future case.

Fixes #2547