py/objint: Allow int() to parse anything with the buffer protocol.

This generalises and simplifies the code and follows CPython behaviour.

See similar change for floats in a07fc5b640.

Signed-off-by: Damien George <damien@micropython.org>

tests/basics/int_parse.py

@@ -0,0 +1,12 @@
+# Test parsing ints.
+
+try:
+    bytearray
+    memoryview
+except NameError:
+    print("SKIP")
+    raise SystemExit
+
+print(int(b"123"))
+print(int(bytearray(b"123")))
+print(int(memoryview(b"123")))