Support attrs alias and private attributes in st.builds

[tybug]

Closes #3791.

More generally, adds support for attr's alias parameter. On master, the following errors, for instance:

@attr.s
class HasAliasedAttribute:
    x: int = attr.ib(alias="crazyname")

st.builds(HasAliasedAttribute)

Attrs also helpfully fills in alias with the correctly-stripped version of private attributes, which is why this fixes the linked issue.

attrs only added alias in 22.2.0. I probably could have thrown a if attrs.__version__ in here and made things backwards compatible, but it would have complicated things, so I've taken the easier option of bumping the dependency. There is precedence for this, but if this is a tough sell I can work on continuing to support previous versions.

P.S. I thought I would take a small break from IR pulls to do some good ol' bug fixing. I'm continuing to work on migrating the datatree to the IR, though! 🙂

[Zac-HD]

Nice work!

[Zac-HD]

I was pretty nervous about this, but checking download stats it seems likely to be fine 🙂