Enable the HWIntrinsic extension methods and remove the instance implementations...

Enable the HWIntrinsic extension methods and remove the instance implementations (#22705)

* Removing various S.R.I.Vector instance method APIs, since they should now be exposed as extension methods

* Updating the JIT to recognize the S.R.I.Vector extension methods.

* Updating various S.R.I.Vector test templates

* Regenerating the S.R.I tests that are created from a template.

* Fixing the numArgs for Base_Vector256_GetLower

* Fixing the handling for `Base_VectorXXX_As` to normalize the struct type.

* Adding the Base_Vector128_As intrinsics back for arm64