Fix a bug when passing data to GMT in Session.open_virtual_file()

[seisman]

Description of proposed changes

External programs like PyGMT can pass dataset/momory to GMT. By default,
GMT can read, modify and free the momery, which sometimes can cause
crashes.

Issue #406 reports an example in which PyGMT crashes. The issue was reported
to the upstream (see GenericMappingTools/gmt#3515
and GenericMappingTools/gmt#3528). It turns out
to be an API user error (i.e., a PyGMT bug).

As per the explanation of Paul, external programs like PyGMT should
always use GMT_IN|GMT_IS_REFERENCE to tell GMT that the data is
read-only, so that GMT won't try to change and free the memory.

This PR makes the change from GMT_IN to GMT_IN|GMT_IS_REFERENCE
in the Session.open_virtual_file() function, updates a few docstrings,
and also adds the script in #406 as a test.

Fixes #406.

GMT C API references: https://docs.generic-mapping-tools.org/latest/api.html#resource-registration

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If adding new functionality, add an example to docstrings or tutorials.

[weiji14]

Cool, the test looks good. Can you edit the top post and add a link/reference to the GMT C API documentation section for GMT_ IN|GMT_IS_REFERENCE (I'm guessing it's https://docs.generic-mapping-tools.org/dev/api.html#resource-registration?) so others know about it in the future.

Anyways, should be good to merge 🎉