check if len of array const arg matches the expected len of the type when lowering to valtree

[sjwang05]

When creating valtrees for arrays passed as const args in lower_const_arg_array, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to lower_const_arg_tup.

fixes #155168

[rustbot]

HIR ty lowering was modified

cc @fmease

[rustbot]

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