[shader builder] improve verification of shaders

porting one of my shaders to qt6, i found one problem by chance: my shader worked for macos/metal, but it did not work on linux/opengl. running macos/opengl i eventually got a run-time error:

Failed to build graphics pipeline state
Failed to link shader program: WARNING: Output of vertex shader 'vTexCoord' not read by fragment shader
ERROR: Input of fragment shader 'texCoord' not written by vertex shader

my vertex shader was using using the output variable vTexCoord

layout(location = 0) in vec4 aVertex;
layout(location = 1) in vec2 aTexCoord;
layout(location = 0) out vec2 vTexCoord;

 
while the fragment shader was using the input variable texCoord

layout(location = 0) in vec2 texCoord;
layout(location = 0) out vec4 fragColor;

the fix for this is obviously simple, the diagnostic not so much (as the opengl driver on linux silently failed instead of giving an error message). so i wonder if rhi could verify the names without relying on the driver?