[Feat] (DirectGLES): emulate GL_TEXTURE_LOD_BIAS in the transpiled ESSL

ES has no per-texture or per-sampler LOD bias at all - GL_TEXTURE_LOD_BIAS is
desktop only, and Vulkan spells it VkSamplerCreateInfo::mipLodBias, which is why
DirectVulkan already honours it. DirectGLES stored the value in sampler state
and then dropped it, so every lookup sampled at the unbiased level of detail.

The bias now reaches the shader as a uniform: a new SPIRV-Cross post-pass
declares one `uniform highp float mg_lodBias_<sampler>;` per mip-capable sampler
and folds it into the level of detail of every lookup that has somewhere to put
it - appended as the bias argument, added to an existing bias, or added to an
explicit textureLod level (Vulkan applies mipLodBias to explicit-LOD fetches too,
and the CTS reference expects the same). texelFetch/textureGather have no bias
by definition, textureGrad offers no argument to fold one into, and the
array-shadow lookups have no bias overload in GLSL at all, so all of those are
left alone. Draws push the bound texture's (or the bound sampler object's, which
overrides it as in GL) value into the uniform, and only when it changed - a
shader whose samplers all have a zero bias issues no extra call at all.

Fixes KHR-GL3{0,2,3}.texture_lod_bias.texture_lod_bias_all.

MobileGL/MG_Backend/DirectGLES/Utils.h

@@ -105,6 +105,18 @@ namespace MobileGL::MG_Backend::DirectGLES {
                                         Uint32 unormOutputMask);
         String ForceFlatIntegerVaryings(const String& glslCode, GLenum shaderType);
         String RemoveLayoutBinding(const String& glslCode);
+        // Prefix of the per-sampler float uniform that carries GL_TEXTURE_LOD_BIAS into
+        // the shader (see EmulateTextureLodBias); the suffix is the sampler's own name.
+        constexpr const char* LOD_BIAS_UNIFORM_PREFIX = "mg_lodBias_";
+        // ES has no per-texture/sampler LOD bias at all (GL_TEXTURE_LOD_BIAS is desktop
+        // only; Vulkan spells it VkSamplerCreateInfo::mipLodBias), so it has to reach the
+        // shader as a uniform and be folded into every lookup's level of detail. Declares
+        // one `uniform highp float mg_lodBias_<sampler>;` per mip-capable sampler and adds
+        // it to the bias / explicit-LOD argument of every lookup that takes one. Draws push
+        // the bound texture's (or sampler object's) value into it; a shader whose samplers
+        // all have a zero bias is therefore unaffected. Returns the source unchanged when
+        // there is nothing to rewrite.
+        String EmulateTextureLodBias(const String& glslCode);
     } // namespace PrgramImpl
 
     namespace Utils {