Change deprecated -fsanitize-recover flag to apply to all sanitizers, not just UBSan.

Summary:
This flag has been deprecated, with an on-by-default warning encouraging
users to explicitly specify whether they mean "all" or ubsan for 5 years
(released in Clang 3.7). Change it to mean what we wanted and
undeprecate it.

Also make the argument to -fsanitize-trap optional, and likewise default
it to 'all', and express the aliases for these flags in the .td file
rather than in code. (Plus documentation updates for the above.)

Reviewers: kcc

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D77753