[MooreToCore] Support for StringType from moore to llvm dialect

[ChenXo0]

Hi! Now I try to add types and operators in sim to get the lowered operators in moore, and then lower them to llvm dialect, so that the corresponding dynamic size container can be implemented in arcilator.

First, add IntType and RefType in sim, as well as VariableOp, BlockAssignOp, Print, ReadOp, and ConcatOp operators.
Taking Variable as an example, creating a stringtype VariableOp in Moore will create an int type through string_constant, and then perform conversionOp to convert the int type to Stringtype, and finally create VariableOp. In sim, if VariableOp can directly accept int type, the conversion time can be saved. Therefore, I think it is not necessary to add StringType separately, and only use Int Type and RefType to represent it.

In sim to llvm dialect, VariableOp will be converted into a series of Ops. First, llvm.alloca will be used to create an i128 memory, which will be divided into i32 size to record the string length, and i96 data to record the string content. Then, llvm.getelementptrOp and llvm.storeOp are used to store the contents in the corresponding locations. This memory will be dynamically doubled according to the length of the string.

Can you give me some advise?