Fix #2005. Allow multiple compilation units to declare identical push_constant blocks (#2123)

* Fixes #2005

Allow multiple units in a stage to have push_constants as long
as the blocks match.
Requires #2006 to be fixed to be functional.

* tweaks to #2005 fix after some testing

* add unit tests for push constants across multiple compilation units

For #2005

* update reference output for tests that fail validation

* fix uninitialized result.validationResult
14 files changed