Merge composition with lambdas

[jfmengels]

Some of our fixes can/could lead to generating composition (f >> g), which could get a bit ugly when one of the functions is a lambda.

I think we could simplify them a bit like this:

(\singleArg -> x |> function) >> g
--> (\singleArg -> x |> function |> g)

f >> (\singleArg -> x |> function)
--> (\singleArg -> x |> f |> function)

We'd also have the symmetrical changes for <<.

I don't think we should do anything when the lambda has multiple arguments, and I don't think we should do anything when both functions are lambdas. At least, I haven't given it enough thought yet.