Test isinf() and isnan() with 64-bit floats

Test isinf() and isnan() with 64-bit floats

This commits adds new tests to the shader common function test group to
check isinf() and isnan() works with 64-bit floats when available.

Minor code refactoring changes affect all common function tests.

New tests:
dEQP-VK.glsl.builtin.function.common.isnan.double*
dEQP-VK.glsl.builtin.function.common.isnan.dvec*
dEQP-VK.glsl.builtin.function.common.isinf.double*
dEQP-VK.glsl.builtin.function.common.isinf.dvec*

Affected tests:
dEQP-VK.glsl.builtin.function.common.*

Components: Vulkan
VK-GL-CTS issue: 2354

Change-Id: Ic63661b6646ccbcda4264660c1633d2f84e9e735