Update NEWS for release

Updating the NEWS file for our next release.  These were some
highlights that I plucked from the commit log but I'm open to adding
or deleting some.

Differential Revision: D933280
Remove some redundant bool parameters

No longer actually used

Differential Revision: D933388
Factor register shuffle algorithm into own module

Factor register shuffle algorithm into own module

Differential Revision: D932183
Removing unnecessary mapping of var ids on CreateCont.

Since D898769, all locals in generator bodies have the same ids
as in the corresponding 'create generator' methods, so the mapping
between these ids is no longer needed.

Differential Revision: D932354
Miscellaneous cleanup

This is all stuff I did while working on guard relaxation
that isn't strictly related to guard relaxation:
- Stop using CheckType with Nullptr.
- Move a bunch of things from ir.cpp to extra-data.cpp and ssa-tmp.cpp.
- Turn DataTypeCategory into an enum class.
- Add folly::FormatValue specializations for JIT::Opcode,
  DataTypeCategory, and any objects with a toString method.
- Kill the Eval.JitCompareHHIR runtime option. Most of the code using
  it is already long gone.
- Add smart::flat_set.
- Clean up MInstrInfo constants, fixing a bug that missed some
  undefined local warnings.
- Assert that the type of IRExtraData subclasses passed to gen()
  matches what the opcode wants.
- Remove unused DontGuardLocal, DontBreakLocal, and DontBreakStack1
  from translator inputs.

Differential Revision: D926849
Fixing typo in zRevRange function

The zRevRange function argument $withscore was referenced
within the function as $withscores. Changed argument name to $withscores
so they match.

Closes #941

Differential Revision: D934709