More file refactoring (#40114)

* Set src in the state functions rather than the toplevel

A good API should only require passing one version of a piece of data
around so do that for src

* Move the rewriting of path into additional_parameter_handling

When the path is a directory we can rewrite the path to be a file inside
of the directory

* Emit a warning when src is used with a state where it should be ignored

changelogs/fragments/file-disallow-src.yaml

@@ -0,0 +1,8 @@
+---
+bugfixes:
+- file module - The file module allowed the user to specify src as a parameter
+  when state was not link or hard.  This is documented as only applying to
+  state=link or state=hard but in previous Ansible, this could have an effect
+  in rare cornercases.  For instance, "ansible -m file -a 'state=directory
+  path=/tmp src=/var/lib'" would create /tmp/lib.  This has been disabled and
+  a warning emitted (will change to an error in Ansible-2.10).