near-vm: Allow straightforward reuse of pre-faulted memory maps for storing executable machine code and wasm memories.

[nagisa]

nearcore's use of the WASM VM is largely single-threaded – it will grab a contract, deserialize it, execute a function therein, and deallocate the resources before moving on.

Today in this scheme one of the cost centres is in creating and faulting-in new memory maps for the executable code and module memory for every contract execution. Our interface should make it possible and straightforward to allocate and prefault the prerequisite memory ahead of time and then just keep writing/reading/executing data from the same memory map.

This, of course, would require to be more careful about e.g. zeroing out the contents of the memory before allowing execution, but it still should be cheaper overall compared to what is being done today.

Related to #8951

[nagisa]

This is solved for executable code. We have also explored this for the data memories, but those have been found to be less obvious of a win. #10851