[PowerRename] Indicate when search field includes leading whitespace

[daverayment]

Description of the new feature / enhancement

In a recent bug report, the user had accidentally copied in a string with a leading space, resulting in no matches being shown (see #35325). This sort of error is very difficult to spot, so it may be useful to show an informational message in the results area when there are no matches and there is leading whitespace in the search term.

There could be some nuance here. For example, should the message always be shown if there is leading whitespace, or only where there would be matches without it being present?

Scenario when this would be used?

This would prevent copy-and-paste issues and would be especially useful for those unfamiliar with the tool.

Supporting information

No response