Display more friendly names for "CCSlice" and "IdleCCSlice" markers

We have `CCSlice` and `IdleCCSlice` markers and we are thinking about whitelisting those so web developers can also see them. But the problem is, it's not really easy to understand what that marker does, especially for web developers. We should either display a more descriptive name for those markers or add a description below their marker name to explain what they do.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-231)