CTAD bug in vector length

**Describe the bug**
Swizzled vector types can't be passed directly to `length()` because `detail::is_gengeohalf::value` is `false` for these types.

From [this StackOverflow question](https://stackoverflow.com/questions/72877944/automatically-convert-sycl-swizzle-operation-to-vector).

**To Reproduce**

``` c++
#define SYCL_SIMPLE_SWIZZLES
#include

using namespace sycl;

int main(){
float3 myVec{1.0, 0.0, 2.0};
auto len = length(myVec.zy());
}
```

The above code fails to compile because it cant deduce typename T of `length` (should be `float2`?) If one instead has
```c++
auto len = length(myVec.zy());
```
it works fine.

**Additional context**

`length()` is defined in builtins.hpp:

``` c++
// float length (gengeofloat p)
template ::value, T>>
float length(T p) __NOEXC {
return __sycl_std::__invoke_length(p);
}
```
and `detail::is_gengeofloat` is only `true` for `type_list, vec, vec, vec>`.

I'm not sure if the solution is to include the SwizzleOp types in `geo_float_list` or to define a specialization for `length` etc for SwizzleOp types, but as the StackOverflow OP points out, this somewhat defeats the purpose of swizzle convenience operations.