Is your feature request related to a problem?

Currently, we use the @Constant annotation to mark parameters as constant (i.e. a literal must be passed). This is an important concept, however, e.g. for partial evaluation or refined types, so a modifier might be better suited.

Desired solution

• Add a const modifier for this purpose.
• For annotations, show an info if the modifier is used, since it is implied. Or should we show an error if it's not used?
• Error if lambda parameters have this modifier
• Error if parameters of callable type have this modifier

Possible alternatives (optional)

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Additional Context (optional)

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