docs(agc): name what shadPS4, fpPS4 and addrlib do for PS4 layered surfaces and display buffers

docs/dev/debt/libSceAgcDriver.md

@@ -81,8 +81,8 @@
 - [sceAgcDriverGetHsOffchipParam](../../../core/libs/prx/libSceAgcDriver/Unimplemented.cpp) (libSceAgcDriver, NID `r28hEh6cNH0`) - declared as a throwing stub. The two `uint16_t` output pointers and integer return type follow [ps5-vulkan](https://github.com/blackbearreloaded/ps5-vulkan/blob/4bb0c8b1423698a7369efc22b829bf16a99e7128/native/tess_driver_import_stub.c#L10), which reads the pair before it binds a tessellation factor ring. The meaning of the two values, their initial state and how they relate to `sceAgcDriverSetHsOffchipParam`, which keeps nothing here, are unknown; the stub does not write caller memory. PPSA99011 imports it
 - [Vertex input and color target overlap](../../../core/libs/prx/libSceAgcDriver/Graphics/src/Draw.cpp) (AGC driver) - direct draws exclude the descriptor prefix skipped by `firstVertex` or `firstInstance` from the alias check; indexed draws conservatively use index zero as the lower bound before adding `firstVertex`. Indirect draws still check the full descriptor extent. Reads of the active target's bytes remain unsupported; same-draw console ordering is not established.
 - [PS4 (GCN) tiling](../../../core/libs/prx/libSceAgcDriver/Graphics/src/TextureTiling.cpp) (libSceAgcDriver, PS4) - not checked on a console. Surfaces with `GuestTextureResource::gcnPitch` set use the GB_TILE_MODE and GB_MACROTILE_MODE tables of [shadPS4](https://github.com/shadps4-emu/shadPS4/blob/main/src/video_core/amdgpu/tiling.cpp) and addrlib's `ComputeSurfaceAddrFromCoordMicroTiled` and `MacroTiled`: 8x8 micro tiles in thin, depth or display element order, macro tiles with pipe config P8_32x32_16x16 (P8_32x32_8x16 for the two PRT thin modes), bank width 1 and a 256-byte pipe interleave, depth micro tiles split into slices a whole surface apart with the bank rotated by (banks / 2 + 1) per slice, PRT pipe and bank taken from the coordinates inside the macro tile, and LINEAR_GENERAL rows of exactly the pitch. [TextureTiling.cpp](../../../core/libs/prx/libSceAgcDriver/tests/TextureTiling.cpp) compares it with a separate implementation of the addrlib formulas.
-- [PS4 (GCN) thick and layered surfaces](../../../core/libs/prx/libSceAgcDriver/Graphics/src/TextureTiling.cpp) (libSceAgcDriver, PS4) - 3D and thick modes (GB_TILE_MODE 15 and 19 to 26) throw, and so does a storage image or a depth plane of a layered surface with several mip levels. A sampled layered surface with several mip levels is stored level by level, which is not checked on a console; [GcnDetile.cpp](../../../core/libs/prx/libSceAgcDriver/tests/execution/GcnDetile.cpp) runs the GPU detiler over every mode that does not throw.
-- [PS4 render targets and display buffers](../../../core/libs/prx/libSceAgcDriver/Execution/src/DisplayBuffer.cpp) (libSceAgcDriver, PS4) - a tiled PS4 display buffer is read as Display2DThin with rows padded to 128 elements, as shadPS4's `image_info.cpp` does. A PS4 render target spans its surface padded to whole macro tiles (1920x1080 at 32 bits is 1920x1088), the display buffer is its top-left corner, and a texture over that corner with the same pitch, tiling and texel size is a [GPU copy](../../../core/libs/prx/libSceAgcDriver/Graphics/src/Texture.cpp) of it. A PS4 `DB_Z_INFO` names a GB_TILE_MODE index; the depth image stays on the GPU and HTILE is kept, as for the PS5.
+- [PS4 (GCN) thick and layered surfaces](../../../core/libs/prx/libSceAgcDriver/Graphics/src/TextureTiling.cpp) (libSceAgcDriver, PS4) - 3D and thick modes (GB_TILE_MODE 15 and 19 to 26) throw, and so does a storage image or a depth plane of a layered surface with several mip levels. A sampled layered surface with several mip levels is stored level by level, which is not checked on a console; [GcnDetile.cpp](../../../core/libs/prx/libSceAgcDriver/tests/execution/GcnDetile.cpp) runs the GPU detiler over every mode that does not throw. The bank of each layer of a tiled 2D array is rotated by (banks / 2 - 1) times the layer index outside the PRT modes, XORed in as AMD's address library and shadPS4 (`tiling.comp`, 0614ce324be0) do; fpPS4 (`ps4_tiling.pas`, 04cefd43e6fd) adds it to the bank instead. Not checked on a console.
+- [PS4 render targets and display buffers](../../../core/libs/prx/libSceAgcDriver/Execution/src/DisplayBuffer.cpp) (libSceAgcDriver, PS4) - a tiled PS4 display buffer is read as Display2DThin with rows padded to 128 elements, as shadPS4's `image_info.cpp` does. A PS4 render target spans its surface padded to whole macro tiles (1920x1080 at 32 bits is 1920x1088), the display buffer is its top-left corner, and a texture over that corner with the same pitch, tiling and texel size is a [GPU copy](../../../core/libs/prx/libSceAgcDriver/Graphics/src/Texture.cpp) of it. A PS4 `DB_Z_INFO` names a GB_TILE_MODE index; the depth image stays on the GPU and HTILE is kept, as for the PS5. shadPS4 (`image_info.cpp`, 0614ce324be0) rounds the width of a tiled display buffer up to a multiple of 128 itself, whereas `DisplayBufferSize` requires the pitch to be one already.
 - [PS4 pattern fill](../../../core/libs/prx/libSceAgcDriver/Execution/src/Driver/Memory/BufferFill.cpp) (libSceAgcDriver, PS4) - the PS4 build of the pattern-fill compute kernel seen in Limbo (CUSA01664), with user data s[4:7] a 32-bit UINT source, s[8:11] the 32-bit UINT destination and s[12:15] a control record of count and index mask, where thread i stores source[i & mask], runs as a GPU fill when the mask is 0, a single repeated dword; other masks run the kernel, since running Limbo's two-dword clears of a 64-bit target as fills made its gameplay advance more slowly per frame. The kernel is recognized by its code, not by an SDK symbol.
 
 ### Functional