showInputBox should allow to change contents based on input

[chrisdias]

vscode.window.showInputBox() lets me accept user input through the command palette, but it is a two step process. I have to first execute a command and then i have to show the input box. Ideally, I should be able to prompt and accept input in one command, much in the way the git branch prompt does:

here i'm prompted with "git checkout", if i have a set of branches they are shown in the list, and I can free form type in any text in order to create a new branch.

As an extension author I would love to be able to have a similar model. For example, let's say I want to have a list of tasks and each task can take a parameter.

myextension create thing1
myextension create thing2

in this case i don't want to select "myextension create thing1" and then have an input box. What i want is to be able to say "myextension thing1 thing1's description". This is also similar to the extension install experience where i can say ext install myextension where myextension is free form text.

[jrieken]

duplicate of #426