SI-7592 Replace s.t.n.u.TreeSet with s.c.m.TreeSet

This means
- migrating usages from the compiler-specific implementation to the
  one in the standard library
- removing the now unused compiler-specific implementation
Updates .gitignore files.
Unseal a uselessly sealed case class.
Seals some case class hierarchies.
Adds a hashCode method to the Settings class for Ant.
Adds equals and hashCode to three classes that implement Ordered.
SI-7591 Move command-line spec usage demo to tests
SI-7591 Minor cleanups
SI-7591 Make s.t.p.n.ConsoleRunner use s.t.c.CommandLine

Before this change s.t.n.u.CommandLine was used instead.

Remove command-line options --ansi, --buildmanager, --show-log
which don't have any effect and don't seem to be used anywhere.
Merge pull request #2692 from soc/SI-7591

SI-7591 Migrate command-line parsing to s.t.cmd
Merge pull request #2694 from adriaanm/master

Merge 2.10.x into master
Merge pull request #2693 from lexspoon/semmle-lint

Lint-like fixes found by Semmle
Merge pull request #2663 from soc/SI-7592

SI-7592 Replace s.t.n.u.TreeSet with s.c.m.TreeSet
typo
prototypical sam support
must check function type first
allow sam to extend FunctionN
only consider sam when arity matches
cleanup, better error messages for arity mismatches
figured out arity checks