conf: support property rules

Add pw_conf_section_update_props_rules() that will not only update the
properties of a section but wil also apply rules in section.rules and
match against the context properties.

Use this by default when using pw_context_conf_update_props().

Add a new method to get a string name of the VM type. Place the
cpu.vm.name in the context properties.

This makes it possible to deprecate the vm.overrides with something more
flexible based on rules. Update the conf files and docs to refect this.

src/modules/module-protocol-pulse.c

@@ -71,11 +71,17 @@
  *     #pulse.min.quantum      = 128/48000     # 2.7ms
  *     #pulse.default.format   = F32
  *     #pulse.default.position = [ FL FR ]
- *     # These overrides are only applied when running in a vm.
- *     vm.overrides = {
- *         pulse.min.quantum = 1024/48000      # 22ms
- *     }
  * }
+ * pulse.properties.rules = [
+ *     {   matches = [ { cpu.vm.name = !null } ]
+ *         actions = {
+ *             update-props = {
+ *                 # These overrides are only applied when running in a vm.
+ *                 pulse.min.quantum = 1024/48000      # 22ms
+ *             }
+ *         }
+ *     }
+ * ]
  *\endcode
  *
  * ### Connection options
@@ -185,19 +191,6 @@
  * This is equivalent to the PulseAudio `default-sample-channels` and
  * `default-channel-map` options in `/etc/pulse/daemon.conf`.
  *
- * ### VM options
- *
- *\code{.unparsed}
- *     vm.overrides = {
- *         pulse.min.quantum = 1024/48000      # 22ms
- *     }
- *\endcode
- *
- * When running in a VM, the `vm.override` section will override the properties
- * in pulse.properties with the given values. This might be interesting because
- * VMs usually can't support the low latency settings that are possible on real
- * hardware.
- *
  * ### Quirk options
  *
  *\code{.unparsed}
@@ -240,6 +233,30 @@
  *     #{ cmd = "load-module" args = "module-gsettings" flags = [ "nofail" ] }
  * ]
  *\endcode
+
+ * ## Dynamic properties
+ *
+ * The pulse.properties can be dyanmically updated with rules. It supports
+ * an `update-props` action. The matches will be performed on the values in
+ * context.properties.
+ *
+ *\code{.unparsed}
+ * pulse.properties.rules = [
+ *     {   matches = [ { cpu.vm.name = !null } ]
+ *         actions = {
+ *             update-props = {
+ *                 # These overrides are only applied when running in a vm.
+ *                 pulse.min.quantum = 1024/48000      # 22ms
+ *             }
+ *         }
+ *     }
+ * ]
+ *\endcode
+ *
+ * In the above example, when running in a VM, the rule will override the properties
+ * in pulse.properties with the given values. This might be interesting because
+ * VMs usually can't support the low latency settings that are possible on real
+ * hardware.
  *
  * ## Stream settings and rules
  *