GrRenderTargetContext scaffolding

I added the renderTargetContext() method to GrTextTarget so I don't
have to convert the entire call stack over in one CL. In the end,
GrTextTarget and GrRenderTargetContext::TextTarget will be deleted.

Change-Id: I49387737c26b69111050101d9da3380617db2918
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/295376
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Herb Derby <herb@google.com>
diff --git a/src/gpu/GrRenderTargetContext.cpp b/src/gpu/GrRenderTargetContext.cpp
index 2a7d6fe..ab69c8a 100644
--- a/src/gpu/GrRenderTargetContext.cpp
+++ b/src/gpu/GrRenderTargetContext.cpp
@@ -108,6 +108,10 @@
         return fRenderTargetContext->fContext;
     }
 
+    GrRenderTargetContext* renderTargetContext() override {
+        return fRenderTargetContext;
+    }
+
     SkGlyphRunListPainter* glyphPainter() override {
         return fRenderTargetContext->glyphPainter();
     }