layout: restructure into src/ tests/ android/ scripts/ tools/

- extension/src/{port,platform,codepage} -> src/; native_render -> src/host
  (+ dxt, shaders/); libgr2 -> src/gr2; extension/third_party -> third_party
- extension/tests -> tests/port, libgr2/tests -> tests/gr2
- android-native -> android (build.sh, push-client.sh moved in)
- script -> scripts; tools/40250 -> tools/server; oracle -> tools/granny-oracle;
  perf tools -> tools/perf
- all build trees under build/ (native, release, android, port-gate)
- xrender:: CMake aliases -> mt::; port-map ledger impl paths rewritten

No code changes. ctest 15/15, port_gate macos+android PASS, port_map check 0 errors.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

third_party/cpython-2.7.18/RISCOS/README

@@ -0,0 +1,36 @@
+This directory contains files for the RISC OS port of Python.
+For more information about RISC OS see http://www.riscos.com/ .
+
+This port is currently being maintained by Dietmar Schwertberger,
+dietmar@schwertberger.de .
+
+On http://www.schwertberger.de you may find compiled versions and libraries
+as well as RISC OS specific documentation and extensions.
+
+
+==========================================================================
+Compiling:
+
+1. Extract Files from archive directory 'Python-...' to a directory named
+   '!Python'.
+2. Use a tool like Rename to change filenames from '*/[ch]' into '[ch].*'.
+3. Create missing directories with 'amu cdirs'.
+4. Build with 'amu'.
+
+I've only tested Acorn/Norcroft C/C++ 5.30 and amu.
+
+Python now uses the 32 bit libraries from Pace as well as the 32 bit
+version of OSLib.
+
+You will also need some additional libraries:
+
+  DLK (patched version)
+    http://www.schwertberger.de
+  OSLib
+    http://www.mk-net.demon.co.uk/oslib
+  
+  zlib (optional)
+    ftp://ftp.freesoftware.com/pub/infozip/zlib/
+  expat (optional)
+    http://sourceforge.net/projects/expat/
+    (makefile and config.h available from http://www.schwertberger.de/riscos_expat.zip