The test being fixed in this commit was flaking with the following
error:
```
Capybara::Ambiguous:
Ambiguous match, found 2 elements matching visible css ".stream-topic-title .title a[href*='/2']"
```
The regexp match on the `href` attribute has the potential to match
multiple elements if both urls contain the `/#{topic.id}` substring. For
example, both `/t/-/2/2` and `/t/-/1/2` will satisfy the regexp.
In core, `escapeExpression` was being applied during the model loading phase. However, plugin consumers of the UserStreamItem component were not necessarily doing the same.
This commit moves the emoji-replacement logic (which also safely handles escaping) into the component template, so that it is safe-by-default, regardless of how it's used by plugins.
