Fix same uniforms in fragment and vertex shaders not working in Metal

[smilediver]

Describe your changes

Context: in OpenGL API setting shader uniforms works at the program level, which means that same named uniforms in vertex and fragment shaders are treated as the same variable, so when you set a uniform it is set in both shaders at once. In Metal API uniforms are set for vertex and fragment shaders separately.

In current Axmol's Metal implementation if you have a same named uniform in vertex and fragment shaders, then only the vertex shader's variable is set, which is different from OpenGL. This PR fixes Metal part to match OpenGL semantics.

This PR may have breaking changes as it modifies UniformLocation and ShaderModuleMTL::getUniformLocation(). But probably it's not a common thing to access UniformLocation internals or calling ShaderModuleMTL::getUniformLocation().

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[halx99]

Please fix the ci check: https://github.com/axmolengine/axmol/actions/runs/8620021129/job/23625989923?pr=1808#step:4:3879

[smilediver]

Pushed fix. Also noticed a uniform type mismatch in positionNormalTexture.vert and colorNormalTexture.frag, so fixed that too.

[halx99]

cheers