UI: Add pause support

Adds support for pausing recordings.  When settings are eligible for
recordings, a pause button will appear next to the recording button.  If
the settings are not eligible, it will warn the user in the output
settings that they cannot pause recordings if those settings are used.

docs/sphinx/reference-frontend-api.rst

@@ -124,6 +124,18 @@ Structures/Enumerations
      the program is either about to load a new scene collection, or the
      program is about to exit.
 
+   - **OBS_FRONTEND_FINISHED_LOADING**
+
+     Triggered when the program has finished loading.
+
+   - **OBS_FRONTEND_EVENT_RECORDING_PAUSED**
+
+     Triggered when the recording has been paused.
+
+   - **OBS_FRONTEND_EVENT_RECORDING_UNPAUSED**
+
+     Triggered when the recording has been unpaused.
+
 .. type:: struct obs_frontend_source_list
 
    - DARRAY(obs_source_t*) **sources**
@@ -402,6 +414,18 @@ Functions
 
 ---------------------------------------
 
+.. function:: void obs_frontend_recording_pause(bool pause)
+
+   :pause: *true* to pause recording, *false* to unpause.
+
+---------------------------------------
+
+.. function:: bool obs_frontend_recording_paused(void)
+
+   :return: *true* if recording paused, *false* otherwise.
+
+---------------------------------------
+
 .. function:: void obs_frontend_replay_buffer_start(void)
 
    Starts replay buffer.