[REF] stock_landed_costs: adapt to valuation layers

We need to increment the value of another layer. We don't  want to write
on this layer in place as we used to do for multiple reasons:
- valuation at date: before the application of an lc, the value should
  not change
- if the layer was consumed, we would need to adapt the consumers and
  if one day we would have needed to understand what happened in the
  fifo stack it would be hell

So we allow to create a valuation layer linked to another valuation
layer through a simple M2O O2M. At the time it is only used on the
landed costs to add value and no quantity so the code expects it would
be the case and it is not enforced. We adapt `_run_fifo` to use the full
value.

We also add a stat button on the landed cost to access the valuation
layers, like what is done for the picking and manufacturing orders.

task-1875873

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