Search file content

### Description of the new feature / enhancement

PowerToys Run can search folders and files; could it also search the contents of a single file? Or could it be a separate tool that can search the contents of files within a specified folder?

### Scenario when this would be used?

I have a folder containing many files. I know one of the files contains a sentence, but I'm unsure which file it is. I want to find that file based on that sentence.

### Supporting information

_No response_

Start by reviewing PowerToys Run's existing file and folder search behavior. Clarify whether content search belongs in PowerToys Run or should be a separate tool, including the supported scope and expected matching behavior. Done means the feature boundaries and acceptance criteria are agreed before implementation.

Written by the indexing model from the issue text.