Enum parameter proposal

[messmerd]

It would be nice if there was a flag in clap_param_info_flags to mark a parameter as an enum.

Take the example of a waveform parameter.
Say the plugin implements this as an integer parameter (min: 0, max: 3) with the 4 integer values mapped to these 4 waveforms: sine, square, saw, triangle. The mapping of each parameter value with each waveform is completely arbitrary, since the integer "2" is unrelated to saw waves, for example. Because of this arbitrary mapping of integer values to specific meanings, this waveform parameter can be considered an "enum" parameter.

For hosts, this information - whether a parameter is an enum or not - can be important to know because it can impact the decision of which type of UI element is best suited for displaying the parameter to users:

• A drop-down list would be ideal for enum parameters but not for regular integer parameters. Each drop-down entry for an enum parameter could be filled with output from the clap_plugin_params.value_to_text function, but a drop-down full of plain integers would not look as good.
• A spinner (numeric updown) would be ideal for integer parameters but not for enum parameters. For enum parameters, what matters most is the text value the integer value is mapped to, not the integer value itself.

Unfortunately, the CLAP standard currently does not provide a way for CLAP hosts to know whether a parameter is an enum or not.
This may be possible through some inadequate (and inefficient) heuristics if the host parses and guesses the meaning of the string clap_plugin_params.value_to_text returns, but clearly that is not desirable.

Luckily, there's a simple and backwards-compatible solution to this dilemma: Add an IS_ENUM flag to the clap_param_info_flags enum.

// ext/params.h
enum {

   // [...]

   // This parameter represents a set of named options mapped to integers.
   // It implies that the parameter is stepped.
   //
   // This flag may help the host decide how to present the parameter to users.
   CLAP_PARAM_IS_ENUM = 1 << 16,
};

If this proposal is accepted, I can create a PR.

[defiantnerd]

I would absolutely support this - I have this issue right now with the AU wrapper where I can not properly match parameter types.
Please create a PR.

[messmerd]

Just created #358