Add backwards compatibility and other fixes to Dispatch macros. (#17996)

Add backwards compatibility and other fixes to Dispatch macros. (#17996)

Summary:
Changes:
1) https://github.com/pytorch/pytorch/pull/17527 changed dispatch macros to be ScalarType based instead of at::Type based.  This broke cpp extensions that relied on dispatch macros.  Since IMO these should be ScalarType based (and some extensions have already updated), we allow either at::Type or at::ScalarType to be passed, but passing at::Type will result in a deprecated warning.

2) Reintroduce macros that were deleted (AT_DISPATCH_ALL_TYPES_AND_HALF, AT_DISPATCH_COMPLEX_TYPES, AT_DISPATCH_ALL_TYPES_AND_HALF_AND_COMPLEX, AT_DISPATCH_ALL_TYPES_AND_COMPLEX); the AND_HALF ones now give a deprecated warning because there are more extensible macros that were introduced in their place.

3) Makes AT_DISPATCH_ALL_TYPES_AND_COMPLEX_AND into a ScalarType based macro (and updates usages).  This was the result of a logical merge conflicts.

4) Adds a new macro, C10_DEPRECATED_MESSAGE for passing a deprecated message to the compiler.  I didn't spend much time seeing if this can be enabled for versions before C++14.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17996

Reviewed By: ezyang

Differential Revision: D14446203

Pulled By: gchanan

fbshipit-source-id: 1da56e2e9c15aa8f913ebbf6bf1110c5b6dc375e