Use Python 3 and bundled re2

Re2 was used bundled anyway and just copying header files from system
doesn't actually change anything, except that it breaks when there is
an API change.

python3.12-imp.patch

@@ -0,0 +1,26 @@
+Description: stop using imp module which was removed in Python 3.12
+Origin: upstream, commits
+ https://chromium.googlesource.com/chromium/src/+/9e0c89a3b5638ba2
+ https://chromium.googlesource.com/chromium/src/+/f5f6e361d037c316
+Last-Update: 2024-03-17
+
+--- a/src/3rdparty/chromium/mojo/public/tools/mojom/mojom/fileutil.py
++++ b/src/3rdparty/chromium/mojo/public/tools/mojom/mojom/fileutil.py
+@@ -3,7 +3,6 @@
+ # found in the LICENSE file.
+ 
+ import errno
+-import imp
+ import os.path
+ import sys
+ 
+--- a/src/3rdparty/chromium/mojo/public/tools/mojom/mojom/parse/lexer.py
++++ b/src/3rdparty/chromium/mojo/public/tools/mojom/mojom/parse/lexer.py
+@@ -2,7 +2,6 @@
+ # Use of this source code is governed by a BSD-style license that can be
+ # found in the LICENSE file.
+ 
+-import imp
+ import os.path
+ import sys
+