Keeps the location of original function definition, and also stores
where it was copied. `functions` and `type` show both locations,
instead of none. It also retains the line numbers in the stack trace.
This would tell you a function was "Defined in - @ line 1" for every
function defined via `source`.
Really, ideally we'd figure out where the *source* call was, but that'
much more complicated, so we just give a comprehensible message.
Changes it from
```
$fish_color_user: not set in local scope
$fish_color_user: set in global scope, unexported, with 1 elements
$fish_color_user[1]: length=3 value=|080|
$fish_color_user: set in universal scope, unexported, with 1 elements
$fish_color_user[1]: length=7 value=|brgreen|
```
(with the trailing empty line - not just a newline)
to
```
$fish_color_user: set in global scope, unexported, with 1 elements
$fish_color_user[1]: |080|
$fish_color_user: set in universal scope, unexported, with 1 elements
$fish_color_user[1]: |brgreen|
```
This stops reading argument names after another option appears. It does not break any previous uses and in fact fixes uses like
```fish
function foo --argument-names bar --description baz
```
* `function` command handles options after argument names (Fixes#6186)
* Removed unneccesary test
