`@TomlMultiline` does not properly escape backslashes during serialization

[inponomarev]

Given:

@Serializable
data class Reproducer(
    @TomlMultiline
    val foo: String
)

val obj = Reproducer("\\\\, \\\"")
val str = Toml.encodeToString(obj)
println(str)

Expectation	Reality
foo = """ \\\\, \\" """	foo = """ \\, \" """

Then, after deserialization,

println(Toml.decodeFromString<Reproducer>(str).foo)

backslashes get "unescaped" and the foo property of the deserialized object is not equal to the original value:

Expectation	Reality
\\, \"	\, "