Backport #18944 to 20.12: Fix mutations text serialization

src/Storages/MutationCommands.cpp

 #include <Storages/MutationCommands.h>
-#include <IO/Operators.h>
+#include <IO/WriteHelpers.h>
+#include <IO/ReadHelpers.h>
 #include <Parsers/formatAST.h>
 #include <Parsers/ExpressionListParsers.h>
 #include <Parsers/ParserAlterQuery.h>
@@ -133,13 +134,13 @@ void MutationCommands::writeText(WriteBuffer & out) const
 {
     WriteBufferFromOwnString commands_buf;
     formatAST(*ast(), commands_buf, /* hilite = */ false, /* one_line = */ true);
-    out << escape << commands_buf.str();
+    writeEscapedString(commands_buf.str(), out);
 }
 
 void MutationCommands::readText(ReadBuffer & in)
 {
     String commands_str;
-    in >> escape >> commands_str;
+    readEscapedString(commands_str, in);
 
     ParserAlterCommandList p_alter_commands;
     auto commands_ast = parseQuery(

tests/queries/0_stateless/01648_mutations_and_escaping.reference

+foo
+foo

tests/queries/0_stateless/01648_mutations_and_escaping.sql

+DROP TABLE IF EXISTS mutations_and_escaping_1648;
+
+CREATE TABLE mutations_and_escaping_1648 (d Date, e Enum8('foo'=1, 'bar'=2)) Engine = MergeTree(d, (d), 8192);
+INSERT INTO mutations_and_escaping_1648 (d, e) VALUES ('2018-01-01', 'foo');
+INSERT INTO mutations_and_escaping_1648 (d, e) VALUES ('2018-01-02', 'bar');
+
+-- slow mutation
+ALTER TABLE mutations_and_escaping_1648 UPDATE e = CAST('foo', 'Enum8(\'foo\' = 1, \'bar\' = 2)') WHERE d='2018-01-02' and sleepEachRow(1) = 0;
+
+-- check that we able to read mutation text after serialization
+DETACH TABLE mutations_and_escaping_1648;
+ATTACH TABLE mutations_and_escaping_1648;
+
+ALTER TABLE mutations_and_escaping_1648 UPDATE e = CAST('foo', 'Enum8(\'foo\' = 1, \'bar\' = 2)') WHERE d='2018-01-02' SETTINGS mutations_sync = 1;
+
+SELECT e FROM mutations_and_escaping_1648 ORDER BY d;
+
+DROP TABLE mutations_and_escaping_1648;