[CIR] Add support for array new with ctor init (#187418)
This adds support for array new initialization that requires calling
constructors.
This diverges a bit from the classic codegen implementation in a couple
of ways. First, we use the cir.array_ctor operation to represent all the
constructor calls that weren't part of an explicit initializer list.
This gets lowered to a loop during the LoweringPrepare pass. Second,
because CIR uses more explicit types, we have to insert a bitcast of the
array pointer to an explicit array type. Third, when an initializer list
is provided and we are calling constructors for the "filler" portion of
the list, we attempt to get the array size as a constant and create a
"tail array" to initialize that is sized to the number of elements
remaining.
