Add flag for enum parameters

[messmerd]

See the proposal here: https://github.com/free-audio/clap/discussions/357

This PR adds a CLAP_PARAM_IS_ENUM flag to clap_param_info_flags to denote an enum parameter.

This flag tells the host when a parameter represents a set of named options mapped to integers, which can help the host decide how to present the parameter to users in its UI.

[CLAassistant]

All committers have signed the CLA.

[defiantnerd]

I think this is really useful PR.

[abique]

Maybe it needs a comment to say that the enum isn't allowed to have "holes" between min and max?

[defiantnerd]

Maybe it needs a comment to say that the enum isn't allowed to have "holes" between min and max?

Maybe, although it should be totally clear. You can't have holes in a normal parameter, too.

[messmerd]

Maybe I could add this wording?

_These named options should be available via value_totext() for each integer value within the parameter's [min, max] range.

[abique]

Maybe I'd put the comment like this.

// Indicates that this parameter represents an enumerated value.
// If you set this flag, then you must set CLAP_PARAM_IS_STEPPED too.
// All values from min to max must have a non blank value_to_text().

[abique]

Thank you :+1:

[baconpaul]

Oh this is great and I'll use it all the time!