goose: support provider cleanup functions

Documented and updated appropriate providers to reflect.

Reviewed-by: Tuo Shan <shantuo@google.com>

internal/goose/testdata/PartialCleanup/foo/goose.go

@@ -0,0 +1,9 @@
+//+build gooseinject
+
+package main
+
+//goose:use Foo
+//goose:use Bar
+//goose:use Baz
+
+func injectBaz() (Baz, func(), error)