feat: add inlay hints for byname parameters

[harpocrates]

This adds => hints for function parameters that are passed by name.
The common case of block by-name arguments moves the => to occur right
after the opening brace instead of before the entire argument.

Implements scalameta/metals-feature-requests#377

[harpocrates]

I'm still not happy with the position of the =>. I'd like it to go on the opening line of a block for a block arg. ie.

Future {/* =>*/
  val x = 1
  x + x
}

It is not yet reliably doing that

[kasiaMarek]

I see that mima fails. You need to add a default to byNameParameters in InlayHintsParams.java. Basically all things in mtags-interfaces need to be backwards compatible, because Metals will use old mtags (presentation compiler) for old Scala versions.

[tgodzik]

LGTM!

[harpocrates]

@tgodzik what's the next sequence of steps I should follow here? Presumably

1. port the change to the scala 3 repo (so it'll work for recent Scala versions)
2. add the knob to the various frontends (so like scalameta/metals-vscode@main...harpocrates:metals-vscode:byname-inlay-hints, but also for nvim-metals and the others)

How do we make sure that everything merged here also makes it to Scala 3? Is it basically up to contributors to be vigilant? Drift seems like it might be annoying. And if that's the process, I should probably also port 7d68a12, right?

[tgodzik]

port the change to the scala 3 repo (so it'll work for recent Scala versions)

We would need to first release the interfaces, I plan to port both this and the other PR for named parameters at the same time most likely.

add the knob to the various frontends (so like scalameta/metals-vscode@main...harpocrates:metals-vscode:byname-inlay-hints, but also for nvim-metals and the others

We usually just port for VS Code relying on other contributors for other repositories. I most cases the settings do not have to be declared in plugins to be used.

How do we make sure that everything merged here also makes it to Scala 3? Is it basically up to contributors to be vigilant? Drift seems like it might be annoying. And if that's the process, I should probably also port 7d68a12, right?

We usually mark it with the backport-scala3-pc label, but I might have missed some recently

[harpocrates]

Thank you, totally makes sense!

[ckipp01]

By the way I'd recommend also making sure this is added to UserConfiguration.scala show it shows up in this page in the docs to help people know it exists if they are setting up a new editor.

[tgodzik]

By the way I'd recommend also making sure this is added to UserConfiguration.scala show it shows up in this page in the docs to help people know it exists if they are setting up a new editor.

Sure! I will add it together with #7400