SoftGPU: Draw sprites that texture from themselves in the GE's pixel order

A sprite that reads what it draws goes through the texture cache pixel by
pixel: rows left to right, top to bottom, texture lines loaded as samples
first read them, and pixels reaching memory a 16-byte block at a time, a
pixel after the next block starts (four with bilinear filtering). Fitted to
geprobe exp81 and exp204-exp209 on hardware; Split Second's blur passes now
match the PSP.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

GPU/Software/RasterizerRectangle.cpp

@@ -342,7 +342,7 @@ void DrawSprite(const VertexData &v0, const VertexData &v1, const BinCoords &ran
 	uint16_t texbufw = state.texbufw[0];
 
 	// We won't flush, since we compile all samplers together.
-	Sampler::FetchFunc fetchFunc = Sampler::GetFetchFunc(state.samplerID, nullptr);
+	Sampler::FetchFunc fetchFunc = state.fetch ? state.fetch : Sampler::GetFetchFunc(state.samplerID, nullptr);
 	_dbg_assert_msg_(fetchFunc != nullptr, "Failed to get precompiled fetch func");
 	auto &pixelID = state.pixelID;
 	auto &samplerID = state.samplerID;