[Feat] (MG_Impl/GLImpl, MG_State): implement glClampColor and glPolygonMode

Fill the two empty // TODO state handlers with GL 3.3 Core-conformant
behavior, backed by new RenderState fields and glGet* read-back.

glClampColor:
- Accept only GL_CLAMP_READ_COLOR (compat GL_CLAMP_VERTEX/FRAGMENT_COLOR
  rejected); clamp is one of GL_TRUE / GL_FALSE / GL_FIXED_ONLY. Note the
  Khronos man page wrongly omits GL_FIXED_ONLY from the accepted set, but
  it is legal AND the default, so it is accepted here.
- Default GL_FIXED_ONLY; both error paths are GL_INVALID_ENUM with no
  state change. glGetIntegerv returns the raw tri-state enum; GetFloatv/
  GetDoublev widen it and GetBooleanv converts nonzero to GL_TRUE via the
  existing fall-through, so one GetIntegerv case serves every getter.

glPolygonMode:
- Core accepts only face == GL_FRONT_AND_BACK (GL_FRONT/GL_BACK were
  removed in 3.1 core); mode is GL_POINT / GL_LINE / GL_FILL. Both errors
  are GL_INVALID_ENUM with no state change.
- Keep separate front/back slots so GL_POLYGON_MODE round-trips its two
  values (identical under a core context). The raster effect (VkPolygonMode
  + fillModeNonSolid) remains a backend follow-up; this is the state layer.

Tests: two RenderStateSanity round-trips; the glClampColor GL_FIXED_ONLY
acceptance assertion is mutation-verified (rejecting it fails the test).
Full SanityTest sweep green (29/29).

MobileGL/MG_State/GLState/RenderState/RenderState.cpp

@@ -103,6 +103,31 @@ namespace MobileGL {
                 return m_parameters.PointSpriteCoordOrigin;
             }
 
+            void RenderState::SetClampReadColor(GLenum clamp) {
+                if (m_parameters.ClampReadColor == clamp) return;
+                m_parameters.ClampReadColor = clamp;
+                ++m_version;
+            }
+
+            GLenum RenderState::GetClampReadColor() const {
+                return m_parameters.ClampReadColor;
+            }
+
+            void RenderState::SetPolygonMode(GLenum front, GLenum back) {
+                if (m_parameters.PolygonModeFront == front && m_parameters.PolygonModeBack == back) return;
+                m_parameters.PolygonModeFront = front;
+                m_parameters.PolygonModeBack = back;
+                ++m_version;
+            }
+
+            GLenum RenderState::GetPolygonModeFront() const {
+                return m_parameters.PolygonModeFront;
+            }
+
+            GLenum RenderState::GetPolygonModeBack() const {
+                return m_parameters.PolygonModeBack;
+            }
+
             void RenderState::SetPointSize(Float size) {
                 if (m_parameters.PointSize == size) return;