Add support for Inlay Hints for (unnamed) parameter names

Hello,
We would all like to see the support for inlay hints.
There isn't much to say here, everything is more or less self explanatory.

[DanTup]

In your previous screenshot there were two places inlay hints were being used:

1. At the call site of functions, to show the names of arguments (that are not already named)
2. Were types are being inferred and not present in the source code

Although both use inlay hints, the implementation of these is quite separate and I think make sense to track separately (for example one could be shipped without the other).

I've updated the name of this issue to assume the first - it's worth filing a separate issue about the other one too.

Right now, use of Inlay Hints is blocked on LSP support which is in progress at microsoft/language-server-protocol#956.

[RedyAu]

I would like to second this issue, would be very useful. VSCode has an inlay hints setting now; maybe the situation has changed since?

Enabling this has no effect for .dart files.

[DanTup]

@RedyAu Dart uses LSP, so nothing could be started on this until it's been available in LSP:

microsoft/language-server-protocol#956

[sanathusk]

The VS Code API has been finalized: microsoft/vscode#16221 (comment). I would love to see the feature implemented in vscode for dart .Vscode already supports it for JavaScript & typescript.