[Fix, Test] (MG_Backend/DirectGLES, MG_Util, MG_Impl): widen three-channel render targets wherever the driver refuses them

Complementary Reimagined would not load through Espryt on Mali: Iris got
GL_FRAMEBUFFER_UNSUPPORTED building its composite framebuffer, because
colortex1 is RGB8_SNORM and colortex2 is RGB16F - three-channel formats
that no real ES driver can render to (EXT_render_snorm covers R/RG/RGBA
only, and the float extensions exclude the RGB forms). The frontend's
probe cache diagnosed this correctly and then had nothing to offer: the
NoThreeChannelRenderTarget widening machinery existed but was gated to
multisample targets alone. llvmpipe turns out to refuse most of the same
attachments - CI retrace stayed green only because a replay never
branches on glCheckFramebufferStatus - so this was never a desktop-vs-
device split, just an unlit path.

The widening now applies to every color-attachable image, renderbuffers
included, riding the driver-probe branch so the native format is still
tried first and substituted only on refusal. One ThreeChannelWidening
table owns the widened (internalformat, format, type) triple per source
format - the previous per-case branches disagreed with each other and
could emit an unuploadable (RGBA16F, GL_RGB, GL_BYTE) combination or
widen into another three-channel format the driver refuses just the
same. Uploads repack three-component client data to four with the
format's own one in the alpha channel (127 is not 1 for RGB8I - the
integer arms carry integer ones); readback drops the synthetic alpha,
derived from the actual image being read, not the bound framebuffer,
so glGetTexImage through a scratch FBO cannot be confused by an
unrelated widened attachment.

Stored alpha on a widened attachment is now an invariant 1.0 rather
than an accident: the color-mask sync clears the alpha bit per draw
buffer (glColorMaski for MRT mixes), and clears route through
glClearBufferfv with alpha substituted on widened slots only -
scissored clears inherit the discipline for free, integer color
buffers keep their explicit integer-clear path, and glGet still
answers the application's own mask. GL_DST_ALPHA blending, blits and
readback therefore all see 1.0 without further interception.

DriverPost grows the rows this bug earned: EXT_color_buffer_float
detection (previously unreferenced anywhere) with a FAIL row when
absent, the missing EXT_render_snorm row, and a three-channel-
attachment row that reports one representative per widening class -
graded so a half-float-only driver warns about the 32-bit float gap
instead of being declared unsupported.

Gates: 606/606 unit at default and with the async kill switch; full
retrace, both backends - the complementary fixtures now run with the
widening ACTIVE on llvmpipe and pass with a slightly better SSIM than
before; ext caselist DirectGLES holds 3914/4867 with zero set drift
while 54 cases move from NotSupported to genuinely passing; on the
Mali-G77 device, Complementary Reimagined builds its pipeline and
renders in-world through Espryt (md5-verified build), BSL still green.
A new ThreeChannelAttachmentScenario pins the frontend answer -
COMPLETE where it used to say UNSUPPORTED - on the real driver.

MobileGL/MG_Util/BackendLoaders/OpenGL/Loader.cpp

@@ -838,6 +838,12 @@ namespace MobileGL::MG_Util::BackendLoader {
                 if (std::strcmp(extension, "GL_EXT_render_snorm") == 0) {
                     caps.SupportsRenderSnorm = true;
                 }
+                if (std::strcmp(extension, "GL_EXT_color_buffer_float") == 0) {
+                    caps.SupportsColorBufferFloat = true;
+                }
+                if (std::strcmp(extension, "GL_EXT_color_buffer_half_float") == 0) {
+                    caps.SupportsColorBufferHalfFloat = true;
+                }
                 if (std::strcmp(extension, "GL_EXT_sRGB_write_control") == 0) {
                     caps.SupportsSrgbWriteControl = true;
                 }

MobileGL/MG_Util/BackendLoaders/OpenGL/Loader.h

@@ -1034,6 +1034,16 @@ namespace MobileGL {
             // GL_EXT_render_snorm is present, so the signed-normalized formats are colour-renderable
             // (and usable as multisample texture storage) rather than texture-only.
             Bool SupportsRenderSnorm = false;
+            // GL_EXT_color_buffer_float is present, so GL_RGBA16F / GL_RGBA32F / GL_R11F_G11F_B10F
+            // (and the R/RG float formats) are colour-renderable. ES 3.x core makes them
+            // texture-only, and every Iris shaderpack renders into at least R11F_G11F_B10F, so
+            // without this no shaderpack can work at all.
+            Bool SupportsColorBufferFloat = false;
+            // GL_EXT_color_buffer_half_float is present: the half-float subset of the above, for
+            // drivers that ship only the smaller extension. Note it does NOT rescue GL_RGB16F -
+            // the extension nominally lists it but disclaims it under ES 3.x, and real drivers
+            // reject it, which is why three-channel float attachments are widened instead.
+            Bool SupportsColorBufferHalfFloat = false;
             // GL_EXT_sRGB_write_control is present, so GL_FRAMEBUFFER_SRGB can be turned off.
             // GLES has no such switch in core: writes into an sRGB attachment are ALWAYS encoded,
             // while desktop GL leaves GL_FRAMEBUFFER_SRGB disabled by default and writes raw.