river-layout: update to v3

- Remove advertise_view and advertise_done events. Using the information
provided by these for any purpose would make the layout far less
predictable. Futhermore, in the months this has been available for use,
to my knowledge nobody has actually used it for anything useful.

- Replace the set/mod layout value events with a single user_command
event. This simplifies the protocol and is more flexible for clients.

- Add a layout_name argument to the commit request. This name is an
arbitrary, user-facing string that might, for example, be displayed by a
status bar. This was present in early drafts of the protocol, but was
removed in favor of river-options. Since river-options itself has since
been removed and this feature is nice to have, re-add it.

- Rename main factor to main ratio in rivertile. The "factor" name was
just legacy from dwm, "ratio" is much more accurate.

doc/riverctl.1.scd

@@ -90,15 +90,11 @@ over the Wayland protocol.
 	Set the layout namespace of currently focused output, overriding
 	the value set with *default-layout* if any.
 
-*set-layout-value* _namespace_ _type_ _name_ _value_
-	Set the value with name _name_ of the layout on the focused output
-	with matching namespace. If there is no matching layout, this command
-	does nothing.
-
-*mod-layout-value* _namespace_ _type_ _name_ _value_
-	Modify the value with name _name_ of the layout on the focused
-	output with matching namespace. If there is no matching layout,
-	this command does nothing.
+*send-layout-cmd* _namespace_ _command_
+	Send _command_ to the layout client on the currently focused output
+	with the given _namespace_, if any. What commands a layout client
+	understands depends on the layout client. For rivertile, see the
+	documentation in the *rivertile*(1) man page.
 
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