More command tweaks

[dualspiral]

SpongeAPI | Sponge Impl

While I've got a minute...

• Introduces ValueParameter.Simple which is primarily used to allow the use of Mojang provided parameters that we wrap - they don't need to know about the CommandContext.Builder so this allows third party frameworks to use the Mojang provided parameters.

  Note that aspirationally, at some point I might associate a ClientCompletionKey with each of these to make it clear what parameter links to what key - again, a QoL thing for third party consumers.

  This will fix the issue in Inherite from default parameters in a more restrictive way #2290 insofar as composition is concerned, though the next point will make that moot.

• Adds a ValueParameterModifier that modifies the output/completions of a parameter. This is generally going to be easier than trying to recreate a parameter (such as entities) itself.

  I have not allowed for the transformation of parameter types. As well as it being difficult to do because of the more strongly typed system we have, it's not really encouraged that non-parsing logic should go in a parser - they should do the minimum to validate that a parameter is valid for the context - if a later parameter fails then the work in the parser is wasted and so it is best to do as much work as possible in the executor, when you have a guarantee that your transformations will be used.

  This should be a better way of solving the issue in Inherite from default parameters in a more restrictive way #2290 and basically sidestep the problem in Missing ClientCompletionTypes #2289.