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/gpu/effects/GrConfigConversionEffect.cpp b/src/gpu/effects/GrConfigConversionEffect.cpp
index bedcc78..4743f34 100644
--- a/src/gpu/effects/GrConfigConversionEffect.cpp
+++ b/src/gpu/effects/GrConfigConversionEffect.cpp
@@ -31,7 +31,7 @@
         fragBuilder->codeAppendf("%s;", tmpDecl.c_str());
 
         fragBuilder->codeAppendf("%s = ", tmpVar.c_str());
-        fragBuilder->appendTextureLookup(args.fSamplers[0], args.fCoords[0].c_str(),
+        fragBuilder->appendTextureLookup(args.fTexSamplers[0], args.fCoords[0].c_str(),
                                        args.fCoords[0].getType());
         fragBuilder->codeAppend(";");