binder: Cross-user channels require SDK R+ today but they could be made to work for system apps on P & Q as well

[jdcormie]

bindServiceAsUser() is public in R but exists as a @SystemApi since L. However, to support server pre-auth we also need resolveServiceAsUser(). We could access this via createContextAsUser() in R and via createPackageContextAsUser() on P and Q.

[kannanjgithub]

Marking this for Next.