This makes it easier to spot syntax errors when editing the
class reference. The schema is referenced locally so validation
can still work offline.
Each class XML's schema conformance is also checked on GitHub Actions.
area_shape_entered and area_shape_exited had the exact same description. Changed area_shape_exited's description to specify that the signal is emitted when another area's shape exits rather than enters this area's shapes.
Fix some typoed names from the doc
Add _index to "index" parameters of *_shape_* signals, this is both in doc and in the template. This makes the code, signature and doc easier to understand
Add method to get Node from the _index params of those signals. This was not as easy to find as one would expect. Putting this information where it is needed will help.
For the time being we don't support writing a description for those, preferring
having all details in the method's description.
Using self-closing tags saves half the lines, and prevents contributors from
thinking that they should write the argument or return documentation there.
