Deterministic assembly creation

[Thealexbarney]

With the recent changes done in Roslyn to allow reproducible builds, it would be useful in il-repack had that option as well.

As far as I can tell, there are at least 3 things preventing this, with 2 of them requiring changes to Cecil:

1. New names of renamed types This could be probably handled by producing a GUID from a hash of some of the type/assembly/etc. values.
2. The generated assembly's MVID Roslyn uses a hash of the assembly as a source for the MVID
3. The PE timestamp Roslyn also uses a hash for this field with the upper bit set dotnet/coreclr#1615