feature: support appending title to crossref with trailing `.`

### Is your feature request related to a problem? Please describe. <!-- A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]. --> My mkdocstrings-python-xref project extends this handler and supplies a richer syntax for cross-references. In looking at our internal projects that use this feature, we have found that we can live without most of that syntax but in addition to the leading `.` syntax supported by this handler, we do extensively use the trailing `.` syntax proposed here, which has not analogous support in this hander. We also often refer to symbols that are not imported locally so we cannot use the scoped reference feature. Supporting this would allow us to switch to the standard handler, especially in the context of porting our docs to use zensical. ### Describe the solution you'd like <!-- A clear and concise description of what you want to happen. --> Extend the current cross-reference syntax to support appending the title text when the cross-reference ends with a `.` after an identifier. For instance: `[foo][mypackage.]` would be equivalent to `[foo][mypackage.foo]` and `[foo][..sibling.]` would be equivalent to `[foo][..sibling.foo]`. ### Describe alternatives you've considered <!-- A clear and concise description of any alternative solutions or features you've considered. --> Really the only alternative is to convert the references to manually include the title. ### Additional context <!-- Add any other context or screenshots about the feature request here. --> Yes, I know this project is in maintenance mode, but it also seems like it is still providing the support for these features in Zensical. If you think you might be willing to make an exception in this case, let me know and I will submit a PR. I think it is a relatively simple implementation.