v2: Changed SplitPath to return an object when no output parameters are passed. (Approach 3.)

[jeeswg]

Rationale

• The functionality was previously mentioned in Thoughts for v2.0.
• The functionality would be useful in preparing AHK v1 scripts, for subsequent conversion to AHK v2. (With a custom SplitPath backport used in AHK v1.)
• If A_ScriptName will remain as currently defined in AHK v2, it will be a modifiable custom dialog title, not a consistent script file name, therefore SplitPath(A_ScriptFullPath).Name would be the AHK v2 equivalent of AHK v1's A_ScriptName.

Implementation

This approach creates 5 (or fewer) strings, as individual internal variables, and outputs them either to variables, or to an object.

At present, the internal SplitPath function always returns OK.
(The external function returns a blank string as before, else an object.)

See also:
Attempt 1. #276.
Attempt 2. #289. (This was fixed with a 2nd commit, not shown in the PR description.)
Attempt 3. This PR. Third time lucky? (This PR passes the same test code as in #289.)

(Attempts 2 and 3, differ, but both have good ideas.)
(There are just so many approaches and minor considerations.)
If any major changes are needed for the code, and a separate commit is created, that's fine, I don't need to be credited.
I would look forward to seeing the main dev's implementation. Warm regards.