Use SamplerID in place of GLuint handles

Update all Sampler handles to type SamplerID, preparing for midframe
capture of sampler.

Bug: angleproject:3804
Change-Id: I9337919f97d61e28718987612d642c569b90246a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1761780
Commit-Queue: Jiacheng Lu <lujc@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/validationES2.cpp b/src/libANGLE/validationES2.cpp
index d83cbde..6665216 100644
--- a/src/libANGLE/validationES2.cpp
+++ b/src/libANGLE/validationES2.cpp
@@ -2420,7 +2420,7 @@
             return true;
 
         case GL_SAMPLER:
-            if (context->getSampler(name) == nullptr)
+            if (context->getSampler({name}) == nullptr)
             {
                 context->validationError(GL_INVALID_VALUE, kInvalidSamplerName);
                 return false;