When a search in an editor does not yield any results, a status message
with the content "String xyz is not found" with "xyz" being the search
string. It is currently hard to understand which part of the message the
actual search string is and maybe users do not even know the term
"string".

With this change, the message for a search of "xyz" not yielding any
results is changed to: "No search results for: xyz"
This makes clear what the search string is without requiring to quote
it.

Contributes to
https://github.com/eclipse-platform/eclipse.platform.ui/issues/1993