pw_utils: Wait for frame completion before queueing

Without explicit sync, we have no way to signal the PipeWire consumer when the
rendering is done. So, wait until it's done before giving it the frame.

This should fix flickering screencasts on NVIDIA.

wiki/Configuration:-Debug-Options.md

@@ -21,7 +21,6 @@ debug {
     force-pipewire-invalid-modifier
     dbus-interfaces-in-non-session-instances
     wait-for-frame-completion-before-queueing
-    wait-for-frame-completion-in-pipewire
     emulate-zero-presentation-time
     disable-resize-throttling
     disable-transactions
@@ -155,22 +154,6 @@ debug {
 }
 ```
 
-### `wait-for-frame-completion-in-pipewire`
-
-<sup>Since: 25.05</sup>
-
-Wait until every screencast frame is done rendering before handing it over to PipeWire.
-
-Sometimes helps on NVIDIA to prevent glitched frames when screencasting.
-
-This debug flag will eventually be removed once we handle this properly (via explicit sync in PipeWire).
-
-```kdl
-debug {
-    wait-for-frame-completion-in-pipewire
-}
-```
-
 ### `emulate-zero-presentation-time`
 
 Emulate zero (unknown) presentation time returned from DRM.

wiki/Nvidia.md

@@ -42,9 +42,11 @@ The fix shipped in the driver at the time of writing uses a value of 0, while th
 
 ### Screencast flickering fix
 
+<sup>Until: next release</sup>
+
 If you have screencast glitches or flickering on NVIDIA, set this in the niri config:
 
-```kdl
+```kdl,must-fail
 debug {
     wait-for-frame-completion-in-pipewire
 }