Blender Git Loki

Cmake/MSVC: Enable Edit and Continue for debug builds.

This change switches the debug symbol format from /Zi to /ZI for
debug builds of blender, allowing Edit and Continue to work.

This allows limited [1] code changes in the debugger without
having to stop the process and recompile a new binary leading
to improved developer productivity.

All MSVC versions we support support this flag, Clang on
windows does not mind the /ZI flag, but doesn't currently
emit the required information to have this feature work.

[1] https://docs.microsoft.com/en-us/visualstudio/debugger/supported-code-changes-cpp