Always write float output from the shader debug sampling shader

[jeremyg-lunarg]

The debug sampling shader renders into an R32G32B32A32_SFLOAT target but for integer textures, the output variable is declared to be integer. This is undefined behavior and it causes VK_Shader_Debug_Zoo, Section GLSL1, Test 180 to fail when running with KosmicKrisp. There is not a VUID about this, but the Validation layer reports
Undefined-Value-ShaderFragmentOutputMismatch, which is a warning.

The full validation error, which is only reported if you enable warnings (export VK_LAYER_REPORT_FLAGS=error,warn):

Validation Warning: [ Undefined-Value-ShaderFragmentOutputMismatch ] | MessageID = 0xe5642923
vkCreateGraphicsPipelines(): pCreateInfos[0] Inside [VK_SHADER_STAGE_FRAGMENT_BIT], it writes to
  [Output variable, Location 0, "output"] with a numeric type of UINT but VkSubpassDescription::pColorAttachments[0] 
  pointing at VkRenderPassCreateInfo::pAttachments[0] is created with VK_FORMAT_R32G32B32A32_SFLOAT
  (numeric type of FLOAT) which does not match and the resulting values written will be undefined.
Spec information at https://docs.vulkan.org/spec/latest/chapters/interfaces.html#interfaces-fragmentoutput
Objects: 1
    [0] VkShaderModule 0x5b000000005b0

[baldurk]

I don't think this should be fixed with a bitcast on the shader side. Instead we should create one render path per format (SFLOAT/UINT/SINT) so that the native format is respected.

This can keep just the one image & readback path, and do the format cast in the image views. It'll need one image view+framebuffer+renderpass each.