add array element mutex offset in print and gc

[vtjnash]

The layout and printing logic need to correctly offset and align the inset fields to account for the per-element mutex of an atomic array with large elements.

Fix #58993

[oscardssmith]

Does this also need 1.11 backport?

[gbaraldi]

julia> struct CxRL
           condvar::Condition
           x::Int
           lock::ReentrantLock
           CxRL() = new(Condition(), 5, ReentrantLock())
       end

julia> struct OnceHolder
           once::OncePerThread{CxRL}
           OnceHolder() = new(OncePerThread{CxRL}(CxRL))
       end

julia> holder = OnceHolder()
OnceHolder(OncePerThread{CxRL, Type{CxRL}}(CxRL[], UInt8[], CxRL))

julia> if length(ARGS) > 0
           display(holder)
       end

julia> holder.once()
CxRL(Condition(), 5, ReentrantLock())

julia> holder.once.xs[2]

This still hangs

[vtjnash]

Alright, now includes the additional revert required to fix that bug too.

[gbaraldi]

The only issue with reverting that is a performance regression due to llvm's cost modeling pessimizing vectorization if the GEP calculation happens outside the GEP (it's their fault and maybe they will fix this in the future but this makes a bunch of operations regress) #57389