2. No-op backup/restore in BaseFilter.getDefaultFilterWrappers()

### Affected version

HEAD

### Bug description

File: src/main/java/org/apache/maven/shared/filtering/BaseFilter.java, lines 78–81

// backup values
boolean supportMultiLineFiltering = request.isSupportMultiLineFiltering();
request.setSupportMultiLineFiltering(supportMultiLineFiltering);

This reads the supportMultiLineFiltering flag from the request and immediately writes the same value back. The variable supportMultiLineFiltering is never used again. The comment says "backup values" but there is no corresponding restore. This appears to be leftover dead code from an incomplete refactoring.

Open src/main/java/org/apache/maven/shared/filtering/BaseFilter.java and inspect lines 78–81 inside getDefaultFilterWrappers(). Confirm how the supportMultiLineFiltering value is used around this code, remove the unused no-op backup/restore block, and run the project’s test suite to verify filtering behavior remains unchanged.

Written by the indexing model from the issue text.