Fix #24314 - File icons missing for hidden files (#24391)

- **fix ignoring ignored files when matching icons**
- **remove poorly named and confusing method
`PathExt.icon_stem_or_suffix` and refactor
`PathExt.extension_or_hidden_file_name` to actually do what it says it
does**

Closes #24314

Release Notes:

- Fixed an issue where hidden files would have the default icon instead
of the correct one
- Fixed an issue where files with specific icons (such as
`eslint.config.js`) would not have the their specific icon without a
leading `.` (`.eslint.config.js`)