Overload `clip` function for differnt data types

[denisalevi]

Our implementation of the clip function currently casts all arguments to double. When implementing #37, we should also add at least an option for casting to float. Maybe even overload the function for different types as done with the modulo function (while taking care of type safety when comparing different data types).

[denisalevi]

Just saw that brian2 has an issue for clip in cpp standalone as well (brian-team/brian2#782). Just referencing it here since probably the only difference btwn cpp and cuda implementation will be the __host__ __device__ flags I suppose.

[denisalevi]

Brian2 templates just the first arguments (value) and casts the other two (a_min and a_max) to double (merged in brian-team/brian2#810). Makes sense, but we might want an option to cast to float when having #37 implemented, which then is not type save for large integers. If we still want it, it should produce a warning and can probably be implemented similar as done for #45. Either way, we should update this when we next update brian2, which added tests for the clip function to return the same type as the value argument.

[moritzaugustin]

now: only single precision others move to wishlist

[denisalevi]

I implemented a quick fix for single precision: Depending on precision mode (single/double), all argument of clip are now float or double

clip(float value, float min, float max){}
clip(double value, double min, double max){}

This means it is not type safe to pass int32 values in single precision mode. But it is not relevant for our benchmarks (we only pass 0 as integer literal in STDP).

brian2 has templated the value parameter and castst the other to double. brian2genn just used only float, which is not typesafe.