JIT: fix handling of newarr size (#19633)

JIT: fix handling of newarr size (#19633)

`newarr` accepts either an int or native int for array size, and the
newarr helper the jit invokes takes a native int.

If the value on the stack is an int and the jit is running on a platform
where native int is larger than int, the jit must explicitly widen the
int to native int.

Found this while running some code through the interpreter -- the path
the interpreter uses to invoke jitted code doesn't guarantee that int args
are 64 bit clean.