[Feat] (DirectGLES): support rectangle textures where the emulation is exact

ES has no rectangle target and no rectangle sampler, so DirectGLES declared
GL_TEXTURE_RECTANGLE unsupported outright: the texture was never synced or bound,
and SPIRV-Cross refused the shader ("Rectangle textures are not supported on
OpenGL ES") which left the whole program unlinkable.

A rectangle texture is a single-level, clamped 2D texture whose only real
difference is that its lookups take non-normalized coordinates. Where every use
takes *integer* texel coordinates - texelFetch, textureSize - that difference
does not exist at all, and the two are the same thing. So:

- A new SPIR-V pass rewrites Dim::Rect image types to Dim::2D before
  transpiling, and restates the rectangle capabilities as Shader. It declines
  any module containing a normalized-coordinate lookup rather than emitting
  something subtly wrong; SPIRV-Cross then rejects that module exactly as
  before, so nothing that used to work changes and nothing new renders wrongly.
- The target maps to GL_TEXTURE_2D for storage, uploads and binding, alongside
  the existing 1D and 1D-array emulation.

Fixes KHR-GL31.texture_size_promotion.functional outright, which takes GL31 to
100% conformance. GL32/GL33 advance past their rectangle cases to a separate
GL_RGB16 multisample issue. No regressions across texture_swizzle, shaders30,
texture_lod_*, framebuffer_blit, packed_depth_stencil, transform_feedback,
clip_distance or draw_buffers; DirectVulkan re-verified unaffected.

MobileGL/MG_Backend/DirectGLES/Managers.cpp

@@ -3344,6 +3344,17 @@ namespace MobileGL::MG_Backend::DirectGLES {
                     effectiveSpirv = &noperspectiveSpirv;
                 }
 
+                // ES has no rectangle sampler, and SPIRV-Cross refuses the whole module rather
+                // than approximating one. Where every use takes integer texel coordinates a
+                // rectangle image is indistinguishable from a 2D one, so rewrite the type and let
+                // it through; the pass declines anything it cannot convert exactly.
+                Vector<unsigned int> rectLoweredSpirv;
+                if (MG_Util::ShaderTranspiler::ShaderCompiler::LowerRectImagesForEssl(*effectiveSpirv,
+                                                                                       rectLoweredSpirv) &&
+                    !rectLoweredSpirv.empty()) {
+                    effectiveSpirv = &rectLoweredSpirv;
+                }
+
                 MG_Util::ShaderTranspiler::SpvcSession spvcSession(*effectiveSpirv,
                     MG_Util::ShaderTranspiler::SessionUsageBit::Transpile);