Rename EmitArgs::fSamplers to fTexSamplers

Renames fSamplers to fTexSamplers in GrProcessor EmitArgs, and renames
GrGLSLTextureSampler to GrGLSLSampler. This will allow us to add a
second array of buffer samplers.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1862373003

Review URL: https://codereview.chromium.org/1862373003
diff --git a/src/effects/SkMorphologyImageFilter.cpp b/src/effects/SkMorphologyImageFilter.cpp
index d6e7dfa..d0ca205 100644
--- a/src/effects/SkMorphologyImageFilter.cpp
+++ b/src/effects/SkMorphologyImageFilter.cpp
@@ -239,7 +239,7 @@
     }
     fragBuilder->codeAppendf("\t\tfor (int i = 0; i < %d; i++) {\n", width);
     fragBuilder->codeAppendf("\t\t\t%s = %s(%s, ", args.fOutputColor, func, args.fOutputColor);
-    fragBuilder->appendTextureLookup(args.fSamplers[0], "coord");
+    fragBuilder->appendTextureLookup(args.fTexSamplers[0], "coord");
     fragBuilder->codeAppend(");\n");
     // coord.x += pixelSize;
     fragBuilder->codeAppendf("\t\t\tcoord.%s += %s;\n", dir, pixelSizeInc);