layers:Update some pool_node naming

Change some pool_node names to pool_state in DescriptorSet class.
Also update getPool function prototype to the new name of
getDescriptorSetState().
diff --git a/layers/descriptor_sets.cpp b/layers/descriptor_sets.cpp
index dc647e2..5f92749 100644
--- a/layers/descriptor_sets.cpp
+++ b/layers/descriptor_sets.cpp
@@ -1498,24 +1498,24 @@
             }
         }
     }
-    auto pool_node = getPoolNode(dev_data, p_alloc_info->descriptorPool);
+    auto pool_state = getDescriptorPoolState(dev_data, p_alloc_info->descriptorPool);
     // Track number of descriptorSets allowable in this pool
-    if (pool_node->availableSets < p_alloc_info->descriptorSetCount) {
+    if (pool_state->availableSets < p_alloc_info->descriptorSetCount) {
         skip_call |= log_msg(
             report_data, VK_DEBUG_REPORT_ERROR_BIT_EXT, VK_DEBUG_REPORT_OBJECT_TYPE_DESCRIPTOR_POOL_EXT,
-            reinterpret_cast<uint64_t &>(pool_node->pool), __LINE__, DRAWSTATE_DESCRIPTOR_POOL_EMPTY, "DS",
+            reinterpret_cast<uint64_t &>(pool_state->pool), __LINE__, DRAWSTATE_DESCRIPTOR_POOL_EMPTY, "DS",
             "Unable to allocate %u descriptorSets from pool 0x%" PRIxLEAST64 ". This pool only has %d descriptorSets remaining.",
-            p_alloc_info->descriptorSetCount, reinterpret_cast<uint64_t &>(pool_node->pool), pool_node->availableSets);
+            p_alloc_info->descriptorSetCount, reinterpret_cast<uint64_t &>(pool_state->pool), pool_state->availableSets);
     }
     // Determine whether descriptor counts are satisfiable
     for (uint32_t i = 0; i < VK_DESCRIPTOR_TYPE_RANGE_SIZE; i++) {
-        if (ds_data->required_descriptors_by_type[i] > pool_node->availableDescriptorTypeCount[i]) {
+        if (ds_data->required_descriptors_by_type[i] > pool_state->availableDescriptorTypeCount[i]) {
             skip_call |= log_msg(report_data, VK_DEBUG_REPORT_ERROR_BIT_EXT, VK_DEBUG_REPORT_OBJECT_TYPE_DESCRIPTOR_POOL_EXT,
-                                 reinterpret_cast<const uint64_t &>(pool_node->pool), __LINE__, DRAWSTATE_DESCRIPTOR_POOL_EMPTY,
+                                 reinterpret_cast<const uint64_t &>(pool_state->pool), __LINE__, DRAWSTATE_DESCRIPTOR_POOL_EMPTY,
                                  "DS", "Unable to allocate %u descriptors of type %s from pool 0x%" PRIxLEAST64
                                        ". This pool only has %d descriptors of this type remaining.",
                                  ds_data->required_descriptors_by_type[i], string_VkDescriptorType(VkDescriptorType(i)),
-                                 reinterpret_cast<uint64_t &>(pool_node->pool), pool_node->availableDescriptorTypeCount[i]);
+                                 reinterpret_cast<uint64_t &>(pool_state->pool), pool_state->availableDescriptorTypeCount[i]);
         }
     }