[Feat] (MG_Impl, MG_Backend): implement the integer direct state access framebuffer clears

glClearNamedFramebufferiv and glClearNamedFramebufferuiv were stubs, so a clear through
them was silently dropped and the attachment kept whatever it held. Their float siblings
were already implemented, which is what made the gap look like a rendering bug rather than
a missing entry point.

Which buffers they accept is narrower than glClearNamedFramebufferfv and differs between
the two: signed values clear COLOR or STENCIL, unsigned only COLOR (GL 4.6 core 17.4.3.1).
Only the colour buffer is indexed, so a stencil clear naming any drawbuffer other than 0 is
INVALID_VALUE rather than merely ignored, and anything else is INVALID_ENUM. Resolving the
framebuffer by name goes through the same helper the float forms use, which is what reports
INVALID_OPERATION for a name that is neither zero nor an existing framebuffer.

Both backends express them the way they already express the float forms: DirectGLES binds
the named framebuffer and forwards to glClearBuffer*, Magma queues the payload against the
named framebuffer rather than the bound one.

direct_state_access.framebuffers_clear_errors passes on both backends, and
framebuffers_clear passes on Espryt. Magma still fails that one, for a separate reason on
the materialization side rather than in these entry points.

MobileGL/MG_Backend/DirectGLES/BackendObject_DirectGLES.cpp

@@ -988,6 +988,8 @@ namespace MobileGL::MG_Backend::DirectGLES {
             funcsTable.GL.ClearBufferuiv = ClearBufferuiv;
             funcsTable.GL.ClearBufferiv = ClearBufferiv;
             funcsTable.GL.ClearNamedFramebufferfv = ClearNamedFramebufferfv;
+            funcsTable.GL.ClearNamedFramebufferiv = ClearNamedFramebufferiv;
+            funcsTable.GL.ClearNamedFramebufferuiv = ClearNamedFramebufferuiv;
             funcsTable.GL.ClearNamedFramebufferfi = ClearNamedFramebufferfi;
             funcsTable.GL.BlitFramebuffer = BlitFramebuffer;
             funcsTable.GL.BlitNamedFramebuffer = BlitNamedFramebuffer;