port 2P step 1: vendor CPython 2.7.18 as the mtpython static library

The embedded 40250 script layer needs its own interpreter on five platforms.
2.7 is end-of-life, so nothing can be fetched from the target SDKs and the
source is vendored (official 2.7.18 tarball, trimmed to 25MB; Lib/ stays for
step 3's python27.zip).

cpython-2.7.18/CMakeLists.txt builds one `mtpython` static library from exactly
the 133 objects the reference libpython2.7.a contains, off by default behind
-DMTGODOT_EMBED_PYTHON=ON. The source list and the built-in module table
(config/config.c, 39 entries) are shared; pyconfig.h is a probe result and is
not, so each platform keeps its own under config/<platform>/, regenerated by
tools/py_embed/gen_pyconfig.sh and checked against the shared table.

Three vendor patches, documented in docs/THIRD-PARTY.md: configure/configure.ac
learn arm64 on macOS, and posixmodule.c undefines the process-control calls it
hard-defines past pyconfig.h when building for iOS.

macOS (ctest python.embed: every builtin imports, codecs and pickle work off the
vendored Lib/), Android arm64 and iOS arm64 build. Linux needs a Linux host and
Windows needs a MinGW-vs-MSVC decision; both are noted for step 4.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

extension/third_party/cpython-2.7.18/Lib/encodings/charmap.py

@@ -0,0 +1,69 @@
+""" Generic Python Character Mapping Codec.
+
+    Use this codec directly rather than through the automatic
+    conversion mechanisms supplied by unicode() and .encode().
+
+
+Written by Marc-Andre Lemburg (mal@lemburg.com).
+
+(c) Copyright CNRI, All Rights Reserved. NO WARRANTY.
+
+"""#"
+
+import codecs
+
+### Codec APIs
+
+class Codec(codecs.Codec):
+
+    # Note: Binding these as C functions will result in the class not
+    # converting them to methods. This is intended.
+    encode = codecs.charmap_encode
+    decode = codecs.charmap_decode
+
+class IncrementalEncoder(codecs.IncrementalEncoder):
+    def __init__(self, errors='strict', mapping=None):
+        codecs.IncrementalEncoder.__init__(self, errors)
+        self.mapping = mapping
+
+    def encode(self, input, final=False):
+        return codecs.charmap_encode(input, self.errors, self.mapping)[0]
+
+class IncrementalDecoder(codecs.IncrementalDecoder):
+    def __init__(self, errors='strict', mapping=None):
+        codecs.IncrementalDecoder.__init__(self, errors)
+        self.mapping = mapping
+
+    def decode(self, input, final=False):
+        return codecs.charmap_decode(input, self.errors, self.mapping)[0]
+
+class StreamWriter(Codec,codecs.StreamWriter):
+
+    def __init__(self,stream,errors='strict',mapping=None):
+        codecs.StreamWriter.__init__(self,stream,errors)
+        self.mapping = mapping
+
+    def encode(self,input,errors='strict'):
+        return Codec.encode(input,errors,self.mapping)
+
+class StreamReader(Codec,codecs.StreamReader):
+
+    def __init__(self,stream,errors='strict',mapping=None):
+        codecs.StreamReader.__init__(self,stream,errors)
+        self.mapping = mapping
+
+    def decode(self,input,errors='strict'):
+        return Codec.decode(input,errors,self.mapping)
+
+### encodings module API
+
+def getregentry():
+    return codecs.CodecInfo(
+        name='charmap',
+        encode=Codec.encode,
+        decode=Codec.decode,
+        incrementalencoder=IncrementalEncoder,
+        incrementaldecoder=IncrementalDecoder,
+        streamwriter=StreamWriter,
+        streamreader=StreamReader,
+    )