When using the SVE API, Unsafe.SizeOf on a vector always return 128bits.

Instead, the value should return the current vector length of the machine. For example, Neoverse N2 has 128bits, whereas Neoverse V1 has 256bits.

There are quite a few places within the jit that make 128bit assumptions. These need to instead use the current vector length.

Once merged, #101295 will by default set the vector length of the machine to 128bits. This needs partially reverting so that the default option is to not change the current setting.

When all the above is fixed, all the of HardwareIntrinsics_Arm tests should pass on a Neoverse V1.