Switch to using in-mem sequence generator only when explicitly configured in connection string. Move spanner-related functions to pkg/util/spanner. (#103363)

* Switch to using in-mem sequence generator only when explicitly configured in connection string.
Move spanner-related functions to pkg/util/spanner.

pkg/util/spanner/spanner.go

@@ -0,0 +1,40 @@
+// Package spanner should only be used from tests, or from enterprise code (eg. protected by build tags).
+package spanner
+
+import (
+	"strconv"
+
+	spannerdriver "github.com/googleapis/go-sql-spanner"
+	"google.golang.org/api/option"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+)
+
+func UsePlainText(connectorConfig spannerdriver.ConnectorConfig) bool {
+	if strval, ok := connectorConfig.Params["useplaintext"]; ok {
+		if val, err := strconv.ParseBool(strval); err == nil {
+			return val
+		}
+	}
+	return false
+}
+
+// ConnectorConfigToClientOptions is adapted from https://github.com/googleapis/go-sql-spanner/blob/main/driver.go#L341-L477, from version 1.11.1.
+func ConnectorConfigToClientOptions(connectorConfig spannerdriver.ConnectorConfig) []option.ClientOption {
+	var opts []option.ClientOption
+	if connectorConfig.Host != "" {
+		opts = append(opts, option.WithEndpoint(connectorConfig.Host))
+	}
+	if strval, ok := connectorConfig.Params["credentials"]; ok {
+		opts = append(opts, option.WithCredentialsFile(strval))
+	}
+	if strval, ok := connectorConfig.Params["credentialsjson"]; ok {
+		opts = append(opts, option.WithCredentialsJSON([]byte(strval)))
+	}
+	if UsePlainText(connectorConfig) {
+		opts = append(opts,
+			option.WithGRPCDialOption(grpc.WithTransportCredentials(insecure.NewCredentials())),
+			option.WithoutAuthentication())
+	}
+	return opts
+}