Import fbpacktool from AOSP

* qc_image_unpacker doesn't support Pixel 6, this does

Source: https://developers.google.com/android/binary_transparency/pixel#fbpacktool
Change-Id: If7a409ed9f84e9c8ff43a8aa3d26eaae2c8a0640

fbpacktool/packedstruct.py

@@ -0,0 +1,61 @@
+# Copyright 2021 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+import struct
+
+
+class PackedStruct(object):
+    """Class representing a C style packed structure
+
+    Derived classes need to provide a dictionary with key will be the attributes and the values are
+    the format characters for each field. e.g.
+
+    class Foo(PackedStruct):
+        _FIELDS = {
+            x: 'I',
+            name: '64s',
+        }
+
+    In this case Foo.x will represent an "unsigned int" C value, while Foo.name will be a "char[64]"
+    C value
+
+    """
+
+    def __init__(self, *args, **kwargs):
+        self._fmt = '<' + ''.join(fmt for fmt in self._FIELDS.values())
+        for name in self._FIELDS:
+            setattr(self, name, None)
+
+        for name, val in zip(self._FIELDS.keys(), args):
+            setattr(self, name, val)
+        for name, val in kwargs.items():
+            setattr(self, name, val)
+
+    def __repr__(self):
+        return '{} {{\n'.format(self.__class__.__name__) + ',\n'.join(
+            '    {!r}: {!r}'.format(k, getattr(self, k)) for k in self._FIELDS) + '\n}'
+
+    def __str__(self):
+        return struct.pack(self._fmt, *(getattr(self, x) for x in self._FIELDS))
+
+    def __bytes__(self):
+        return struct.pack(self._fmt, *(getattr(self, x) for x in self._FIELDS))
+
+    def __len__(self):
+        return struct.calcsize(self._fmt)
+
+    @classmethod
+    def from_bytes(cls, data):
+        fmt_str = '<' + ''.join(fmt for fmt in cls._FIELDS.values())
+        return cls(*struct.unpack(fmt_str, data))