Compute bounds union while combining path range draw path batches

Compute bounds union while combining batches generated by NVPR device
independent text code-path. Otherwise the overlap test of the
GrDrawTarget::recordBatch violate painter's algorithm order.
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Review URL: https://codereview.chromium.org/1894973008

src/gpu/batches/GrDrawPathBatch.cpp

@@ -102,6 +102,7 @@ bool GrDrawPathRangeBatch::onCombineIfPossible(GrBatch* t, const GrCaps& caps) {
         draw->fY = head->fY;
         that->fDraws.popHead();
     }
+    this->joinBounds(that->fBounds);
     return true;
 }