Octal escape sequences can be wrong formatted in C++, Java and Python

[mikir]

Zserio version and language
Zserio: 2.16.0
Language: C++/Java/Python

Describe the bug
Zserio has different definition of octal escape sequences in string literals compared to C++, Java or Python. Zserio definition is as follows:

• '\0[0-3]oo` where o is octal diggit, but [0-3] is optional and the last octal diggit 'o' is optional as well.

This allows writing the following string literal in Zserio:

"This is octal \0156"

Generators do not convert such octal number which results to the same string literal which is not valid in Java, C++ and Python. This is because Java, C++ and Python do support octal escape sequences in string literal in the following format:

• '\ooo' where o is octal diggit

How to reproduce
Please, see an example schema here.

Expected behavior
Generators should convert Zserio octal escape sequences to the correct format.