Show available params when using in-app translation dialog

[Anty0]

When a developer creates a translation for the first time using the translation dialog triggered by ALT+Click, there is no indication of which parameters are available. From a UX point of view, it might be better to show available placeholders to the user and allow the user to drag and drop them, similar to how we already allow this when translating existing strings.
We should also use the first parameter name as the default plural parameter name.