[AST][RecoveryExpr] Build recovery expressions by default for C++.

Reland https://reviews.llvm.org/D76696
All known crashes have been fixed, another attemption.

We have rolled out this to all internal users for a while, didn't see
big issues, we consider it is stable enough.

Reviewed By: sammccall

Subscribers: rsmith, hubert.reinterpretcast, ebevhan, jkorous, arphaman, kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D78350