Let "return" exit a script (#8148)

Currently, if a "return" is given outside of a function, we'd just
throw an error.

That always struck me as a bit weird, given that scripts can also
return a value.

So simply let "return" outside also exit the script, kinda like "exit"
does.

However, unlike "exit" it doesn't quit an interactive shell - it seems
weird to have "return" do that as well. It sets $status, so it can be
used to quickly set that, in case you want to test something.

doc_src/cmds/return.rst

@@ -17,6 +17,7 @@ Description
 
 It is usually added inside of a conditional block such as an :ref:`if <cmd-if>` statement or a :ref:`switch <cmd-switch>` statement to conditionally stop the executing function and return to the caller, but it can also be used to specify the exit status of a function.
 
+If run at the top level of a script, it exits that script and returns the given status, like :ref:`exit <cmd-exit>`. If run at the top level in an interactive session, it will set ``$status``, but not exit the shell.
 
 Example
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