new `createParam` utility

[stackoverfloweth]

This utility effectively already existed under the private asParamGetSet function. This PR renames that to createParam and adds a defaultValue argument with overloads that retain the correct type for ParamWithDefault.

This small utility enables developers to create custom params slightly more easily.

createParam((value, { invalid }) => {
  if (value === 'asc' || value === 'desc') {
    return value
  }

  throw invalid()
}, 'asc')

The value of this utility really comes in the setting of default values. Without this utility, developers will need to define their custom ParamGetSets with satisfies ParamGetSet<MyType> to prevent losing the fact that the param has a default value. Without doing so, when accessing the routes params developers will find the type is MyType | undefined even though we know it has a default value.

The first argument is any Param, the second is an optional default value.

createParam(Boolean, true)

It also allows developers to add a default value to existing params.

createParam(MySortParam, 'asc')

If the param is a ParamGetSet with a default value it will be replaced.

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