jule: implement immutable strings

[mertcandav]

Description

This PR implements immutable strings for Jule. Primitive string type is mutable, which is performs copying and heap allocations, even for literals. The purpose is reduce copying and heap allocations for strings, especially for literals. Thus, program can share common allocation without allocate new copy of string because it's immutable.

For mutable strings and efficient concats, the StrBuilder struct added to std::string package. The + operator is still supported for primitive string type, but it performs allocation without capacity, so is not efficient especially for big strings.

The old implementation is C++ STL based, new implementation is Jule's RC based. It still guarantees NULL-terminated strings like C. So, using with Integrated Jule should be work as expected without any modification.

Performance

On my primary system (MacBook M2 Pro), average execution time of Jule compiler for whole Jule compiler source code is ~0.48s, after immutable strings is ~0.54s. I think it is possible that this performance loss is due to the loss of optimizations that C++ STL offers for std::basic_string, which is used by old implementation. However, considered as reasonable performance lost. If it caused by bad handling of immutable strings, it will be improved at the future.

Changelog

• Some optimizations are removed which is enabled by --opt-str
• std::strings: add the StrBuilder
• Strings are performs RC now
• api: fix: jule::to_str<T> function define declared as jule::to_str2<T>