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/Misc/TextMate/Python-Dev.tmbundle/Commands/Build.tmCommand

@@ -0,0 +1,25 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>beforeRunningCommand</key>
+	<string>nop</string>
+	<key>command</key>
+	<string># XXX TODO
+# - Highlight any compiler warnings for Python code.
+# - Point out if compile failed.
+
+cd $TM_PROJECT_DIRECTORY
+make -s -j2 2&gt;&amp;1 | pre
+
+rescan_project</string>
+	<key>input</key>
+	<string>none</string>
+	<key>name</key>
+	<string>Build Python</string>
+	<key>output</key>
+	<string>showAsHTML</string>
+	<key>uuid</key>
+	<string>B545BB1B-A8E1-426C-B50A-426E78B96D38</string>
+</dict>
+</plist>