fsmonitor: migrate Python ABCs from collections to collections.abc

The Collections Abstract Base Classes in the collections module are
deprecated since Python 3.3 in favor of collections.abc, and removed
in Python 3.10.

hgext/fsmonitor/pywatchman/pybser.py

@@ -36,6 +36,7 b' import sys'
 
 from . import compat
 
+abc = collections.abc
 
 BSER_ARRAY = b"\x00"
 BSER_OBJECT = b"\x01"
@@ -207,9 +208,7 b' class _bser_buffer:'
             self.ensure_size(needed)
             struct.pack_into(b"=cd", self.buf, self.wpos, BSER_REAL, val)
             self.wpos += needed
-        elif isinstance(val, collections.Mapping) and isinstance(
-            val, collections.Sized
-        ):
+        elif isinstance(val, abc.Mapping) and isinstance(val, abc.Sized):
             val_len = len(val)
             size = _int_size(val_len)
             needed = 2 + size
@@ -260,9 +259,7 b' class _bser_buffer:'
             for k, v in iteritems:
                 self.append_string(k)
                 self.append_recursive(v)
-        elif isinstance(val, collections.Iterable) and isinstance(
-            val, collections.Sized
-        ):
+        elif isinstance(val, abc.Iterable) and isinstance(val, abc.Sized):
             val_len = len(val)
             size = _int_size(val_len)
             needed = 2 + size