Add an assist/refactor to remove a function tear-off

[rrousselGit]

Hello!

One of Dart's feature is the ability to pass a function identifier to another function as argument, such as:

list.map(callback);

But it's not uncommon that after some changes, our callback now expects two arguments. Meaning we have to remove the tear-off to write instead:

list.map((e) => callback(e, anotherParam));

Similar to how we have a "replace function literal with tear-off" refactor, it would be nice to have a "replace tear-off with function literal".
This would enable quickly doing a back-and-forth between both options depending on how the code evolves

[bwilkerson]

I could easily see an assist to convert

list.map(callback);

to

list.map((e) => callback(e));

and we could easily detect when the tear-off required more parameters, but how would we know what the other arguments ought to be?

[rrousselGit]

I would assume that the refactor would specify the new arguments. It would simply unwrap the tear-off, and have users specify the new arguments themselves.