gh-35838: FriCAS spkg-configure and Feature
As FriCAS is only used as an executable, this is straightforward; quite
a number of systems has Fricas 1.3.8, so this is useful, too.
The FriCAS pexpect interface now uses the new `Executable` feature to
determine the absolute pathname of the fricas executable (unless
executed remotely).
This is made possible by a simple refactor of the
`sage.interfaces.expect.Expect` class: Computing the effective command
line is no longer done in `set_server_and_command` (called by
`__init__`); it is delayed until an interface is started and needs the
command line.
- Fixes #35837
- Fixes #33575
Dependencies: The changes in `sage.interfaces` outside of `.expect` and
`.fricas` are all from the following PR and do not need review.
- Depends on #36656 (merged here)
URL: https://github.com/sagemath/sage/pull/35838
Reported by: Dima Pasechnik
Reviewer(s): Dima Pasechnik, François Bissey, Matthias Köppe
