Change signatures of filter bounds methods to return a rect.

Change filterBounds(), onFilterBounds() and onFilterNodeBounds() and computeFastBounds() to
return the destination rectangle. There was no code path that could
return false, and returning rects by value is ok now.

BUG=skia:5094
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1823573003

Review URL: https://codereview.chromium.org/1823573003
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index 3acb913..3efb44c 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -1077,7 +1077,7 @@
     const SkMatrix& ctm = fMCRec->fMatrix;  // this->getTotalMatrix()
 
     if (imageFilter) {
-        imageFilter->filterBounds(clipBounds, ctm, &clipBounds);
+        clipBounds = imageFilter->filterBounds(clipBounds, ctm);
         if (bounds && !imageFilter->canComputeFastBounds()) {
             bounds = nullptr;
         }