Ambiguous description of `CL_FLT_MIN`, etc.

The description of `CL_FLT_MIN` (and `CL_DBL_MIN` / `CL_HALF_MIN`) is currently:

> Minimum value of type cl_float

"Minimum value" in this case could refer to the smallest floating-point value (meaning, a positive value closest to zero) or the most negative floating-point value (meaning, the value closest to negative infinity). We should clarify this.

In the headers, this is a positive value closest to zero:

https://github.com/KhronosGroup/OpenCL-Headers/blob/6137cfbbc7938cd43069d45c622022572fb87113/CL/cl_platform.h#L192

```c++
#define CL_FLT_MIN 1.175494350822287507969e-38f
```

The description in cppreference (for the analogous `FLT_MIN`) is:

https://en.cppreference.com/w/cpp/types/climits.html

> minimum normalized positive value of float, double and long double respectively

Start with the linked CL/cl_platform.h definitions for CL_FLT_MIN, CL_DBL_MIN, and CL_HALF_MIN, then find their descriptions in the OpenCL documentation sources. Clarify that these constants are the smallest positive normalized floating-point values, and confirm all three descriptions use unambiguous wording.

Written by the indexing model from the issue text.