* AnsiChar/WideChar basic types, "string" alias forbidden in System unit.
Prepare for Unicode/Ansi RTL:
- Compiler defines AnsiChar and WideChar as basic types. Definition of Char is now an alias in the system unit.
- Use of "string" alias in system unit is now forbidden to avoid ambiguity: only unambiguous types can be used.
- Strings that will need to adapt to Unicode/Ansi RTL are now declared as RTLString.