Change how we handle unions of missings and other types in unitary functions

[oxinabox]

Follow up to #53602 (comment)
all the related need_to_handle_undef_sparam should now pass if this is right

[oscardssmith]

is this ready to merge?

[oxinabox]

It seems the CI failures are legit

[martinholters]

Aren't the ::Type{Missing} methods still needed? (Or a branch to deal with T==Missing to avoid calling nonmissingtype_checked on it.)
OTOH, the ::Type{Any} might not be needed anymore to prevent a stack overflow, as the nonmissingtype_checked will throw in the ::Type{>:Missing} method. (But the more specific error might still be worth it.)

[DilumAluthge]

It seems the CI failures are legit

Yes, it looks like the CI failures are related to the changes in this PR.

@oxinabox Are you still interested in working on this? If not, @oscardssmith would you be interested in taking over this PR?

I'm asking because I see the forget me not label here.

[oxinabox]

this is still a change we should have.
I would appreciate it if @oscardssmith took it over

[DilumAluthge]

CI failures seem related to the contents of this PR.

@oscardssmith can I assign this PR for you to take over as the new PR "author"? And to take a look at the failing tests?

[oscardssmith]

will investigate.

[DilumAluthge]

Some more test failures:

Error in testset missing:
Test Failed at /cache/build/tester-amdci5-12/julialang/julia-master/julia-fc50b93d31/share/julia/test/missing.jl:233
  Expression: zero(Missing) === missing
   Evaluated: Missing === missing
Error in testset missing:
Test Failed at /cache/build/tester-amdci5-12/julialang/julia-master/julia-fc50b93d31/share/julia/test/missing.jl:234
  Expression: one(Missing) === missing
   Evaluated: Missing === missing
Error in testset missing:
Test Failed at /cache/build/tester-amdci5-12/julialang/julia-master/julia-fc50b93d31/share/julia/test/missing.jl:235
  Expression: oneunit(Missing) === missing
   Evaluated: Missing === missing

[vtjnash]

CI failure looks unrelated, just waiting for the Windows builders to actually get around to running