[llvm-c] Add C API methods to match 64bit ArrayType C++ API signatures

Fixes https://github.com/llvm/llvm-project/issues/56496.

As mentioned in the issue, new functions LLVMArrayType2 and
LLVMGetArrayLength2 are created so as to not break the old API.
The old methods are then marked as deprecated and callers are
updated.

Differential Revision: https://reviews.llvm.org/D143700