Set array size only after allocating the new memory portion (#58848)

The `.size` of an array might be getting set too early; before the
memory is actually allocated, resulting in larger race windows for
inconsistencies (in particular, during finalizers on this thread) to
manifest. This helps keep those instructions more nearly consecutive to
each other so there is a smaller window for races to be visible, in
typical non-adversarial situations.

Author: MilesCranmer

base/array.jl

@@ -1145,12 +1145,13 @@ function _growbeg!(a::Vector, delta::Integer)
     len = length(a)
     offset = memoryrefoffset(ref)
     newlen = len + delta
-    setfield!(a, :size, (newlen,))
     # if offset is far enough advanced to fit data in existing memory without copying
     if delta <= offset - 1
         setfield!(a, :ref, @inbounds memoryref(ref, 1 - delta))
+        setfield!(a, :size, (newlen,))
     else
         @noinline _growbeg_internal!(a, delta, len)
+        setfield!(a, :size, (newlen,))
     end
     return
 end
@@ -1200,11 +1201,11 @@ function _growend!(a::Vector, delta::Integer)
     len = length(a)
     newlen = len + delta
     offset = memoryrefoffset(ref)
-    setfield!(a, :size, (newlen,))
     newmemlen = offset + newlen - 1
     if memlen < newmemlen
         @noinline _growend_internal!(a, delta, len)
     end
+    setfield!(a, :size, (newlen,))
     return
 end
 
@@ -1222,7 +1223,6 @@ function _growat!(a::Vector, i::Integer, delta::Integer)
     memlen = length(mem)
     newlen = len + delta
     offset = memoryrefoffset(ref)
-    setfield!(a, :size, (newlen,))
     newmemlen = offset + newlen - 1
 
     # which side would we rather grow into?
@@ -1232,11 +1232,13 @@ function _growat!(a::Vector, i::Integer, delta::Integer)
         newref = @inbounds memoryref(mem, offset - delta)
         unsafe_copyto!(newref, ref, i)
         setfield!(a, :ref, newref)
+        setfield!(a, :size, (newlen,))
         for j in i:i+delta-1
             @inbounds _unsetindex!(a, j)
         end
     elseif !prefer_start && memlen >= newmemlen
         unsafe_copyto!(mem, offset - 1 + delta + i, mem, offset - 1 + i, len - i + 1)
+        setfield!(a, :size, (newlen,))
         for j in i:i+delta-1
             @inbounds _unsetindex!(a, j)
         end
@@ -1250,6 +1252,7 @@ function _growat!(a::Vector, i::Integer, delta::Integer)
         unsafe_copyto!(newref, ref, i-1)
         unsafe_copyto!(newmem, newoffset + delta + i - 1, mem, offset + i - 1, len - i + 1)
         setfield!(a, :ref, newref)
+        setfield!(a, :size, (newlen,))
     end
 end
 
@@ -1265,11 +1268,11 @@ function _deletebeg!(a::Vector, delta::Integer)
         @inbounds _unsetindex!(a, i)
     end
     newlen = len - delta
+    setfield!(a, :size, (newlen,))
     if newlen != 0 # if newlen==0 we could accidentally index past the memory
         newref = @inbounds memoryref(a.ref, delta + 1)
         setfield!(a, :ref, newref)
     end
-    setfield!(a, :size, (newlen,))
     return
 end
 function _deleteend!(a::Vector, delta::Integer)