Since ImmutableDictionary and ImmutableSortedDictionary are both
implemented via trees; you can think of an ImmutableDictionary as just
being a sorted dictionary where the underlying key is the hash int.
Since our hash is just a hash of a GUID, we can compare by the GUID,
switch to a ImmutableSortedDictionary, and then avoid another sort
when we're computing checksums.

make sure we use ordered list of document/projectIds when creating checksum
make sure we set HasAllInformation when creating projectInfo

added unit test

now, update time on typing is most of time 0 ms on roslyn solution.

removed serializedSolution/Project/DocumentInfo and rolled them into …

separated checksum creation from ISolutionSynchronizationService

now all solution checksum data is moved down to solution states. and ISolutionSynchrnoizationService will only do synchrnoization between 2 hosts.