[Core Config] Use absl::Invocable instead of std::function (#34282)

Splitting off from https://github.com/grpc/grpc/pull/34273

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BUILD

@@ -2469,6 +2469,7 @@ grpc_cc_library(
     srcs = [
         "//src/core:lib/config/core_configuration.cc",
     ],
+    external_deps = ["absl/functional:any_invocable"],
     language = "c++",
     public_hdrs = [
         "//src/core:lib/config/core_configuration.h",

src/core/BUILD

@@ -2627,6 +2627,7 @@ grpc_cc_library(
     hdrs = [
         "lib/surface/channel_init.h",
     ],
+    external_deps = ["absl/functional:any_invocable"],
     language = "c++",
     deps = [
         "channel_stack_type",

src/core/lib/config/core_configuration.cc

@@ -49,7 +49,8 @@ CoreConfiguration::CoreConfiguration(Builder* builder)
       certificate_provider_registry_(
           builder->certificate_provider_registry_.Build()) {}
 
-void CoreConfiguration::RegisterBuilder(std::function<void(Builder*)> builder) {
+void CoreConfiguration::RegisterBuilder(
+    absl::AnyInvocable<void(Builder*)> builder) {
   GPR_ASSERT(config_.load(std::memory_order_relaxed) == nullptr &&
              "CoreConfiguration was already instantiated before builder "
              "registration was completed");

src/core/lib/config/core_configuration.h

@@ -18,7 +18,8 @@
 #include <grpc/support/port_platform.h>
 
 #include <atomic>
-#include <functional>
+
+#include "absl/functional/any_invocable.h"
 
 #include <grpc/support/log.h>
 
@@ -98,7 +99,7 @@ class CoreConfiguration {
 
   // Stores a builder for RegisterBuilder
   struct RegisteredBuilder {
-    std::function<void(Builder*)> builder;
+    absl::AnyInvocable<void(Builder*)> builder;
     RegisteredBuilder* next;
   };
 
@@ -154,7 +155,7 @@ class CoreConfiguration {
   // Attach a registration function globally.
   // Each registration function is called *in addition to*
   // BuildCoreConfiguration for the default core configuration.
-  static void RegisterBuilder(std::function<void(Builder*)> builder);
+  static void RegisterBuilder(absl::AnyInvocable<void(Builder*)> builder);
 
   // Drop the core configuration. Users must ensure no other threads are
   // accessing the configuration.

src/core/lib/surface/channel_init.h

@@ -21,10 +21,11 @@
 
 #include <grpc/support/port_platform.h>
 
-#include <functional>
 #include <utility>
 #include <vector>
 
+#include "absl/functional/any_invocable.h"
+
 #include "src/core/lib/channel/channel_stack_builder.h"
 #include "src/core/lib/surface/channel_stack_type.h"
 
@@ -41,7 +42,7 @@ class ChannelInit {
  public:
   /// One stage of mutation: call functions against \a builder to influence the
   /// finally constructed channel stack
-  using Stage = std::function<bool(ChannelStackBuilder* builder)>;
+  using Stage = absl::AnyInvocable<bool(ChannelStackBuilder* builder) const>;
 
   class Builder {
    public:

test/core/config/core_configuration_test.cc

@@ -16,6 +16,7 @@
 
 #include <algorithm>
 #include <chrono>
+#include <functional>
 #include <thread>
 #include <vector>