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/GrStrokeRectOp.cpp b/src/gpu/ops/GrStrokeRectOp.cpp
index d8eeab5..b120195 100644
--- a/src/gpu/ops/GrStrokeRectOp.cpp
+++ b/src/gpu/ops/GrStrokeRectOp.cpp
@@ -195,7 +195,7 @@
                                                  renderPassXferBarriers, colorLoadOp);
     }
 
-    void onPrepareDraws(Target* target) override {
+    void onPrepareDraws(GrMeshDrawTarget* target) override {
         if (!fProgramInfo) {
             this->createProgramInfo(target);
         }
@@ -445,7 +445,7 @@
                              GrXferBarrierFlags renderPassXferBarriers,
                              GrLoadOp colorLoadOp) override;
 
-    void onPrepareDraws(Target*) override;
+    void onPrepareDraws(GrMeshDrawTarget*) override;
     void onExecute(GrOpFlushState*, const SkRect& chainBounds) override;
 
 #if GR_TEST_UTILS
@@ -543,7 +543,7 @@
                                              colorLoadOp);
 }
 
-void AAStrokeRectOp::onPrepareDraws(Target* target) {
+void AAStrokeRectOp::onPrepareDraws(GrMeshDrawTarget* target) {
 
     if (!fProgramInfo) {
         this->createProgramInfo(target);