support constant string

[stewpend0us]

msg file:

string NAME0="string value 0"

works fine for c++ but not working in c#. here's the message I get:

Unable to parse field defined as 'FieldDeclaration { Type = string, Identifier = NAME0, Value = "string value 0", IsArray = False, ArrayLength = , InlineComment = , IsUpperBounded = False }': Invalid constant value type 'string'.

[stewpend0us]

test_msgs/msg/Strings.msg