VisualStudio: move PCH rules to projects when possible.
This dramatically helps reduce the size of the solution files when PCH is enabled, since 2 entries per source file are removed. This also corrects a subtle issue where when UNITY + PCH was enabled, the PCH would not be used if a user explicitly tried to compile a source file from outside the unity group. This is possible via the compile source option in the Visual Studio GUI.
Showing with 47 additions and 19 deletions