Optimize FingerprintFilter to directly append to termAttribute, improving performance and reducing memory usage.

### Description

While going through code, found another small optimization that we can do to improve performance and reduce memory footprint.

https://github.com/apache/lucene/blob/88f79193b1884f2cba5399ecde3cd0dd7f7ef793/lucene/analysis/common/src/java/org/apache/lucene/analysis/miscellaneous/FingerprintFilter.java#L176

Raising a PR to address the same.

Start in lucene/analysis/common/src/java/org/apache/lucene/analysis/miscellaneous/FingerprintFilter.java at the linked code near line 176, and inspect how termAttribute is currently populated. Verify that the optimization preserves the filter's existing output while avoiding the unnecessary intermediate allocation, then run the relevant analysis tests.

Written by the indexing model from the issue text.