text: Title: Replace _compat.cached_property with functools.cached_property
  Body: **Description of the issue**
  
  cirq uses an internal version of cached_property defined here to support earlier versions of Python.
  
  https://github.com/quantumlib/Cirq/blob/d33b1a71ac9721e762a2fa1b9e9871edfe187a3c/cirq-core/cirq/_compat.py#L64-L67
  
  As of #6167 we require Python 3.9 which is guaranteed to have [functools.cached_property](https://docs.python.org/3/library/functools.html#functools.cached_property).
  
  We can therefore replace all instances of `_compat.cached_property` with `functools.cached_property` and remove the `cached_property` definition from the _compat.py.
  
  
  **Cirq version**
  
  1.4.0 at d33b1a71ac9721e762a2fa1b9e9871edfe187a3c