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/SkLightingImageFilter.cpp b/src/effects/SkLightingImageFilter.cpp
index 77ea520..e60e7ed 100644
--- a/src/effects/SkLightingImageFilter.cpp
+++ b/src/effects/SkLightingImageFilter.cpp
@@ -1824,7 +1824,7 @@
                                   le.domain(),
                                   temp.c_str(),
                                   texCoords,
-                                  args.fSamplers[0]);
+                                  args.fTexSamplers[0]);
             fragBuilder->codeAppendf("m[%d] = %s.a;", index, temp.c_str());
             index++;
         }