Help: Make some tweaks to documentation around policy scope
In separate commits, this MR:
- Replaces
.. code-block::
with.. signature::
for command signatures incommand/cmake_policy.rst
- Replaces an ambiguous use of "This command" in the docs for
set(PARENT_SCOPE)
with a reference to the command in question. - Clarifies the description of how the policy stack is managed, when using
block(SCOPE_FOR POLICY)