improve inferrability of sort!

[ranocha]

I improved type stability to fix some invalidations. This is based on the following code:

julia> import Pkg; Pkg.activate(temp=true); Pkg.add("Static")

julia> using SnoopCompileCore; invalidations = @snoopr(using Static); using SnoopCompile

julia> length(uinvalidated(invalidations))
195

julia> trees = invalidation_trees(invalidations)
...
 inserting !(::False) in Static at ~/.julia/packages/Static/maaLb/src/Static.jl:428 invalidated:
 ...
                 34: signature Tuple{typeof(!), Any} triggered MethodInstance for Base.Sort.var"#sort!#8"(::Base.Sort.Algorithm, ::typeof(isless), ::Function, ::Nothing, ::Base.Order.ForwardOrdering, ::typeof(sort!), ::Vector) (10 children)
...
                 37: signature Tuple{typeof(!), Any} triggered MethodInstance for Base.Sort.var"#sort!#8"(::Base.Sort.Algorithm, ::typeof(isless), ::typeof(identity), ::Nothing, ::Base.Order.ForwardOrdering, ::typeof(sort!), ::AbstractVector) (15 children)
...
                 39: signature Tuple{typeof(!), Any} triggered MethodInstance for Base.Sort.var"#sort!#8"(::Base.Sort.Algorithm, ::typeof(isless), ::typeof(identity), ::Nothing, ::Base.Order.ForwardOrdering, ::typeof(sort!), ::Vector) (45 children)

With this PR on top of the current release-1.8 branch:

julia> length(uinvalidated(invalidations))
132

and all invalidations in sort! are gone.

This requires a manual backport (which is relatively straightforward) since quite a bit changed in sort.jl - searching for all instances of sub_with_overflow/add_with_overflow in sort.jl and applying the change there.