[ownership] Enable ownership verification by default.

[gottesmm]

[ownership] Enable ownership verification by default.

I also removed the -verify-sil-ownership flag in favor of a disable flag
-disable-sil-ownership-verifier. I used this on only two tests that still need
work to get them to pass with ownership, but whose problems are well understood,
small corner cases. I am going to fix them in follow on commits. I detail them
below:

1. SILOptimizer/definite_init_inout_super_init.swift. This is a test case where
   DI is supposed to error. The only problem is that we crash before we error since
   the code emitting by SILGen to trigger this error does not pass ownership
   invariants. I have spoken with JoeG about this and he suggested that I fix this
   earlier in the compiler. Since we do not run the ownership verifier without
   asserts enabled, this should not affect compiler users. Given that it has
   triggered DI errors previously I think it is safe to disable ownership here.

2. PrintAsObjC/extensions.swift. In this case, the signature generated by type
   lowering for one of the thunks here uses an unsafe +0 return value instead of
   doing an autorelease return. The ownership checker rightly flags this leak. This
   is going to require either an AST level change or a change to TypeLowering. I
   think it is safe to turn this off since it is such a corner case that it was
   found by a test that has nothing to do with it.

rdar://43398898

---

NOTE: This is mostly updating tests. Also I left in part of #23529 b/c I want to start the testing here.

[gottesmm]

@swift-ci test

[gottesmm]

@swift-ci test source compatibility