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
Signed-off-by: dotnet-bot <dotnet-bot@microsoft.com>