[StatsPlugin] Reviewer comments from #36757 (#36787)

Copybara missed the last commit on #36757

Closes #36787

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36787 from yashykt:36757Follow f62cf1eabd
PiperOrigin-RevId: 639933826

src/core/telemetry/metrics.h

@@ -330,7 +330,7 @@ class StatsPlugin {
   virtual void RemoveCallback(RegisteredMetricCallback* callback) = 0;
   // Returns true if instrument \a handle is enabled.
   virtual bool IsInstrumentEnabled(
-      GlobalInstrumentsRegistry::GlobalInstrumentHandle handle) = 0;
+      GlobalInstrumentsRegistry::GlobalInstrumentHandle handle) const = 0;
 
   // Gets a ClientCallTracer associated with this stats plugin which can be used
   // in a call.
@@ -429,7 +429,7 @@ class GlobalStatsPluginRegistry {
     // Returns true if any of the stats plugins in the group have enabled \a
     // handle.
     bool IsInstrumentEnabled(
-        GlobalInstrumentsRegistry::GlobalInstrumentHandle handle) {
+        GlobalInstrumentsRegistry::GlobalInstrumentHandle handle) const {
       for (auto& state : plugins_state_) {
         if (state.plugin->IsInstrumentEnabled(handle)) {
           return true;

src/cpp/ext/otel/otel_plugin.cc

@@ -914,7 +914,7 @@ grpc_core::ServerCallTracer* OpenTelemetryPlugin::GetServerCallTracer(
 }
 
 bool OpenTelemetryPlugin::IsInstrumentEnabled(
-    grpc_core::GlobalInstrumentsRegistry::GlobalInstrumentHandle handle) {
+    grpc_core::GlobalInstrumentsRegistry::GlobalInstrumentHandle handle) const {
   return !absl::holds_alternative<Disabled>(
       instruments_data_.at(handle.index).instrument);
 }

src/cpp/ext/otel/otel_plugin.h

@@ -406,7 +406,7 @@ class OpenTelemetryPlugin : public grpc_core::StatsPlugin {
       override;
   bool IsInstrumentEnabled(
       grpc_core::GlobalInstrumentsRegistry::GlobalInstrumentHandle handle)
-      override;
+      const override;
 
   const absl::AnyInvocable<bool(const grpc_core::ChannelArgs& /*args*/) const>&
   server_selector() const {

test/core/test_util/fake_stats_plugin.h

@@ -361,7 +361,7 @@ class FakeStatsPlugin : public StatsPlugin {
     return nullptr;
   }
   bool IsInstrumentEnabled(
-      GlobalInstrumentsRegistry::GlobalInstrumentHandle handle) override {
+      GlobalInstrumentsRegistry::GlobalInstrumentHandle handle) const override {
     const auto& descriptor =
         GlobalInstrumentsRegistry::GetInstrumentDescriptor(handle);
     return use_disabled_by_default_metrics_ || descriptor.enable_by_default;