Fix implicit fallthroughs throughout Skia.

This CL is not fully comprehensive; for instance, it does not contain
fixes for backends that don't compile on Mac. But it does resolve the
vast majority of cases that trigger -Wimplicit-fallthrough.

A few minor bugs were found and fixed, but none that were likely to
affect normal operation.

Change-Id: I43487602b0d56200ce8b42702e04f66390d82f60
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/295916
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
diff --git a/src/gpu/ops/GrDefaultPathRenderer.cpp b/src/gpu/ops/GrDefaultPathRenderer.cpp
index b05fcdf..88175db 100644
--- a/src/gpu/ops/GrDefaultPathRenderer.cpp
+++ b/src/gpu/ops/GrDefaultPathRenderer.cpp
@@ -583,7 +583,7 @@
             switch (path.getFillType()) {
                 case SkPathFillType::kInverseEvenOdd:
                     reverse = true;
-                    // fallthrough
+                    [[fallthrough]];
                 case SkPathFillType::kEvenOdd:
                     passes[0] = &gEOStencilPass;
                     if (stencilOnly) {
@@ -602,7 +602,7 @@
 
                 case SkPathFillType::kInverseWinding:
                     reverse = true;
-                    // fallthrough
+                    [[fallthrough]];
                 case SkPathFillType::kWinding:
                     passes[0] = &gWindStencilPass;
                     passCount = 2;