Currently the logic to map a section of a file to a location in memory is hand written in storage.cpp for every file in the function PopulateLayout. This is tedious and error prone as it assume this logic needs to be adapted every time we change the structure of the files.

To change this we should capture the logic of figuring out the blocks of memory contained in each file to an own function.

Unblocks mapping separate files in #1947 and makes #4873.