[Perf] (MG_State): remember every dirty rect, not just their union

A Minecraft frame updates ~95 scattered 16x16 sprites in a 1024x512
atlas; MipmapStorage's single union dirty box turned ~95KB of changed
texels into a ~2MB upload on every backend. The storage now keeps a
bounded (96-slot) list of pairwise-disjoint dirty rects BEHIND the
untouched union box: rects cascade-merge on touch or overlap, overflow
folds the pair with minimum enlargement and re-cascades, whole-level
dirties and respecifies just clear the list (empty list = "union box
tells all"). GetDirtyRects hands the list out only when it has 2+
rects, fits the caller's capacity, and its summed area is under 75% of
the union box - fewer driver calls beat equal bytes - so consumers can
never stage more than the union box did.

The list is maintained inside the same four mutation funnels every
texel writer already goes through (MarkDirty, MarkDirtyRegion,
AllocateLevel, TruncateToLevelCount - callers enumerated at the
declaration), so list and union box cannot disagree. Backends OPT IN:
the union-box API and its update order are byte-identical, and an
unmodified backend keeps rendering exactly as before.

96 slots is measured, not guessed: on the bench's 95-sprite lattice a
16-slot list collapses to >93% of the union box, 96 slots reach 4.8%
(~2MB -> ~95KB staged per frame). Verified by a 2859-check fuzz run
against a reference dirty bitmap (union exactness, full coverage,
disjointness, bounds, profitability). Unit tests 421/421.

MobileGL/MG_State/GLState/TextureState/TextureObject2DCube.cpp

@@ -69,6 +69,12 @@ namespace MobileGL {
                 return m_textureStorage.GetDirtyRegion(GetIndexOfTextureUploadTarget(uploadTarget), mipmapLevel);
             }
 
+            SizeT TextureObject2DCube::GetStorageDirtyRects(TextureUploadTarget uploadTarget, Uint mipmapLevel,
+                                                            MipmapDirtyRegion* outRects, SizeT maxRects) const {
+                return m_textureStorage.GetDirtyRects(GetIndexOfTextureUploadTarget(uploadTarget), mipmapLevel,
+                                                      outRects, maxRects);
+            }
+
             void TextureObject2DCube::SetMipmapCompressedImage(TextureUploadTarget uploadTarget, Uint mipmapLevel,
                                                               GLenum internalFormat, const void* data, SizeT size) {
                 m_textureStorage.SetCompressedImage(GetIndexOfTextureUploadTarget(uploadTarget), mipmapLevel,