Switch GrMeshDrawOp::Target to be the stand alone GrMeshDrawTarget class

The Tessellator classes will survive in the NGA and they use
GrMeshDrawOp::Target - but GrMeshDrawOp will not survive.

This is a prelude to making all the remaining GrOp-derived classes OGA-only.

Bug: skia:11837
Change-Id: I62dc92e5f42d672342113f12dcedf3435fab993f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/419198
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
diff --git a/src/gpu/ops/GrFillRRectOp.cpp b/src/gpu/ops/GrFillRRectOp.cpp
index a965055..6251a79 100644
--- a/src/gpu/ops/GrFillRRectOp.cpp
+++ b/src/gpu/ops/GrFillRRectOp.cpp
@@ -53,7 +53,7 @@
         }
     }
 
-    void onPrepareDraws(Target*) final;
+    void onPrepareDraws(GrMeshDrawTarget*) final;
 
     void onExecute(GrOpFlushState*, const SkRect& chainBounds) final;
 
@@ -457,7 +457,7 @@
 
 GR_DECLARE_STATIC_UNIQUE_KEY(gIndexBufferKey);
 
-void FillRRectOp::onPrepareDraws(Target* target) {
+void FillRRectOp::onPrepareDraws(GrMeshDrawTarget* target) {
     // We request no multisample, but some platforms don't support disabling it on MSAA targets.
     if (target->usesMSAASurface() && !target->caps().multisampleDisableSupport()) {
         fProcessorFlags |= ProcessorFlags::kMSAAEnabled;