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/gradients/SkGradientShader.cpp b/src/effects/gradients/SkGradientShader.cpp
index e305a73..6c141dc 100644
--- a/src/effects/gradients/SkGradientShader.cpp
+++ b/src/effects/gradients/SkGradientShader.cpp
@@ -1031,7 +1031,7 @@
                                    const char* gradientTValue,
                                    const char* outputColor,
                                    const char* inputColor,
-                                   const TextureSamplerArray& samplers) {
+                                   const SamplerArray& texSamplers) {
     if (SkGradientShaderBase::kTwo_GpuColorType == ge.getColorType()){
         fragBuilder->codeAppendf("\tvec4 colorTemp = mix(%s, %s, clamp(%s, 0.0, 1.0));\n",
                                  uniformHandler->getUniformVariable(fColorStartUni).c_str(),
@@ -1079,7 +1079,7 @@
                                  uniformHandler->getUniformVariable(fFSYUni).c_str());
         fragBuilder->codeAppendf("\t%s = ", outputColor);
         fragBuilder->appendTextureLookupAndModulate(inputColor,
-                                                    samplers[0],
+                                                    texSamplers[0],
                                                     "coord");
         fragBuilder->codeAppend(";\n");
     }