GL_ARB_enhanced_layouts: mind double types

GL_ARB_enhanced_layouts: mind double types

The special conditions when using the component qualifier with doubles
were not taken into account.

Additionally, the test was reporting a misleading fail due to
non-coherent usage of the "flat" interpolation qualifier. This is now
fixed.

Finally, the generator has been simplified using the refactored code.

Components: OpenGL

VK-GL-CTS issue: 1611

Affects:

KHR-GL44.enhanced_layouts.varying_location_aliasing_with_mixed_auxiliary_storage

Change-Id: I4380ba720f4ea2b2326484d6c8b3e8fc58b1b5e5