feat: get_cwd and set_cwd

[wassup05]

Depends on #1011

1. User facing functions added are

• get_cwd (cwd, err) - Gets the current working directory (cwd) of the process.
• set_cwd (path, err) - Sets the current working directory (cwd) of the process.

2. Binds to getcwd, chdir on Unix and _getcwd, _chdir on Windows
3. Error handling is done through state_type and both the platform specific error code and the user friendly error message are provided if an error occurs

[wassup05]

I am honestly not sure how I should go about testing these functions independently

[sebastian-mutz]

I am honestly not sure how I should go about testing these functions independently

If I uncerstand correctly, it looks like you're already doing that by invoking execute_command_line; that seems like the best solution to me, but perhaps others think of something else..

[wassup05]

Those are commits from the other branch @sebastian-mutz, the one in this PR: #1014

I don't think I can use execute_command_line here, because that spawns a child process to run the command and using cd would change the working directory of that child process not the parent one... But maybe there is some workaround I am not aware of

[sebastian-mutz]

Suggestions for testing (summarising from the chat with Jose):

For testing get_cwd:
gfortran: GETCWD
Intel : GETCWD
Flang: GETCWD

For testing set_cwd:
gfortran: CHDIR
Intel: CHDIR
Flang: CHDIR

Alternatively, using execute_command_line should be fine.

[perazz]

Thank you for this PR @wassup05. Here is a couple of comments:

• the state handler err should be optional. So, the internal handleing features returning the state variable if present, or triggering an error stop if not. This will make behavior consistent to everywhere else.
• For testing: I think set/get can be tested in the same test program imho. Here is an example:

1. get current directory and save it to "pwd" variable -> must be successful
2. create a new local temporary directory -> must be successful
3. set_cwd to that
4. get_cwd should now return the temporary directory
5. set_cwd back to "pwd"
6. check successful

I suggest to merge this PR after directory handling is merged into the library already.

[perazz]

Here are a few additional comments. I suggest the err output variable to be made optional in all cases, consistent with the library. call err0%handle(err) already includes the option to halt on error, if err is not present.

[perazz]

LGTM, thank you @wassup05. As a follow up, may I suggest that the C->Fortran string conversion routine be put, part of a separate PR, into the stdlib_strings module into the to_string interface.

[perazz]

Thank you for this PR, @wassup05. I suggest to wait another couple of days, and in absence of further comments, I think this PR can be merged.