Fixes issue #12472.
This commit doesn't address the underlying issues that come from symbolAnnotationTree using a slightly lower precision coordinate system than the annotations themselves.
Instead, it just puts a small padding around each tile when it queries for tile data, so that symbols right at the tile boundary will be included in both tiles.
The rendering/querying code will take care of only displaying one instance.
The padding is in global coordinates, so at higher zoom the padding will be larger in tile units -- this is consistent with precision loss also being greater at higher zoom.
20f880ebec