Bug 1677466 - Move ParamTraits specializations with extra dependencies out of...

Bug 1677466 - Move ParamTraits specializations with extra dependencies out of IPCMessageUtils.h. r=mccr8

This moves parts of IPCMessageUtils.h to two new header files and adapts
the include directives as necessary. The new header files are:
- EnumSerializer.h, which defines the templates for enum serializers
- IPCMessageUtilsSpecializations.h, which defines template specializations
  of ParamTraits with extra dependencies (building upon both IPCMessageUtils.h
  and EnumSerializer.h)

This should minimize the dependencies pulled in by every consumer of
IPCMessageUtils.h

Differential Revision: https://phabricator.services.mozilla.com/D94459