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/GrBitmapTextGeoProc.cpp b/src/gpu/effects/GrBitmapTextGeoProc.cpp
index b5bae46..246d7be 100644
--- a/src/gpu/effects/GrBitmapTextGeoProc.cpp
+++ b/src/gpu/effects/GrBitmapTextGeoProc.cpp
@@ -66,14 +66,14 @@
         if (cte.maskFormat() == kARGB_GrMaskFormat) {
             fragBuilder->codeAppendf("%s = ", args.fOutputColor);
             fragBuilder->appendTextureLookupAndModulate(args.fOutputColor,
-                                                        args.fSamplers[0],
+                                                        args.fTexSamplers[0],
                                                         v.fsIn(),
                                                         kVec2f_GrSLType);
             fragBuilder->codeAppend(";");
             fragBuilder->codeAppendf("%s = vec4(1);", args.fOutputCoverage);
         } else {
             fragBuilder->codeAppendf("%s = ", args.fOutputCoverage);
-            fragBuilder->appendTextureLookup(args.fSamplers[0], v.fsIn(), kVec2f_GrSLType);
+            fragBuilder->appendTextureLookup(args.fTexSamplers[0], v.fsIn(), kVec2f_GrSLType);
             fragBuilder->codeAppend(";");
             if (cte.maskFormat() == kA565_GrMaskFormat) {
                 // set alpha to be max of rgb coverage