func getAPIClientBuilder(version version.TransportAPI) APIClientBuilder {
	if b, ok := m[version]; ok {
		return b
	}
	return nil
}
getAPIClientBuilder returns the client builder registered for the provided
xDS transport API version.
package xdsclient
import (
	"context"
	"errors"
	"fmt"
	"regexp"
	"sync"
	"time"
	v2corepb "github.com/envoyproxy/go-control-plane/envoy/api/v2/core"
	v3corepb "github.com/envoyproxy/go-control-plane/envoy/config/core/v3"
	"github.com/golang/protobuf/proto"
	"google.golang.org/protobuf/types/known/anypb"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/internal/xds/matcher"
	"google.golang.org/grpc/xds/internal/httpfilter"
	"google.golang.org/grpc/xds/internal/xdsclient/load"
	"google.golang.org/grpc"
	"google.golang.org/grpc/internal/backoff"
	"google.golang.org/grpc/internal/buffer"
	"google.golang.org/grpc/internal/grpclog"
	"google.golang.org/grpc/internal/grpcsync"
	"google.golang.org/grpc/keepalive"
	"google.golang.org/grpc/xds/internal"
	"google.golang.org/grpc/xds/internal/version"
	"google.golang.org/grpc/xds/internal/xdsclient/bootstrap"
)
var (
	m = make(map[version.TransportAPI]APIClientBuilder)
)
func RegisterAPIClientBuilder(b APIClientBuilder) {
	m[b.Version()] = b
}