Extend capabilities of use-package-ensure-function

Extend capabilities of use-package-ensure-function

Modify the expected API of `use-package-ensure-function' so that it is
passed three arguments: the name of the package declared in the
`use-package' form; the argument passed to `:ensure'; and the current
`state' plist created by previous handlers. (Previously, it was only
given a single argument, which was the argument passed to `:ensure',
or the name of the package declared in the `use-package' form, if the
former was `t'.

This allows for more flexibility in the capabilities of the
`use-package-ensure-function' implementation. For example, its
behavior can change depending on the values of other keywords, if
those keywords modify the `state' plist appropriately.