pac solution sync does not have a parameter for blocking deletes

[rajyraman]

pac solution unpack has allowDelete and allowWrite flags, but pac solution sync does not have these flags, which makes this unsuitable when there are multiple developers, each working on their own environment. The current behaviour for pac solution sync is delete everything inside src and recreate.

Please consider adding these two parameters to pac solution sync without which it is very clunky and hard to do solution merging. This is a huge blocker at the moment in multi-developer, multi-environment scenario.