issue: #44961
This PR fixes 3 geometry related bugs:
1. Implement `ToString` interface for GisFunctionFilter.
2. Ignore GisFunctionFilter `MoveCursor` for growing segment.
3. Don't skip null geometry for building R-Tree index, should be record
in null_offsets.
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Signed-off-by: Cai Zhang <cai.zhang@zilliz.com>