Survey of functions returning `bool` under workspace `gstreamer-editing-services`

This is part of an overall effort throughout gstreamer-rs, which started with discussions in #166 (closed) & !196 (closed) (closed) and continued with several merge requests.

The idea is to identify the functions returning a boolean as an indication of a failure and to have them return Result<(), glib::BoolError> instead. The main benefits are:

• Users can use Rust's early exit operator (?), expect or map_err.
• The compiler will issue a warning when the result is not checked.

We decided to use Result<(), gst::LoggableError> when the error is issued in a user implemented function. I didn't find any candidate in gstreamer-editing-services.

Edit: the table was updated further to the feedback from @thiblahute.

Function	Location	Gst Function	Proposed Return Type	Comment
Asset.needs_reload	auto	ges_asset_needs_reload	keep bool	Returns TRUE if the asset was in the cache and could be set as needing reload, FALSE otherwise. Note: See comment from @thiblahute.
Asset.set_proxy	auto	ges_asset_set_proxy	Result<(), glib::BoolError>	Returns TRUE if proxy has been set on asset , FALSE otherwise.
Asset.unproxy	auto	ges_asset_unproxy	Result<(), glib::BoolError>	Returns TRUE if proxy was a known proxy for asset, FALSE otherwise
Clip.move_to_layer	auto	ges_clip_move_to_layer	Result<(), glib::BoolError>	Returns TRUE if clip could be moved FALSE otherwise
Clip.set_top_effect_index	auto	ges_clip_set_top_effect_index	Result<(), glib::BoolError>	Returns TRUE if effect was successfuly moved, FALSE otherwise.
Clip.set_top_effect_priority	auto	ges_clip_set_top_effect_priority	Result<(), glib::BoolError>	No doc.
Extractable.set_asset	auto	ges_extractable_set_asset	Result<(), glib::BoolError>	Returns TRUE if asset could be set FALSE otherwise
Layer.add_clip	auto	ges_layer_add_clip	Result<(), glib::BoolError>	Returns TRUE if the clip was properly added to the layer, or FALSE if the layer refuses to add the clip.
Layer.get_auto_transition	auto	ges_layer_get_auto_transition	keep bool	Returns TRUE if transitions are automatically added, else FALSE. Note: See comment from @thiblahute.
Layer.remove_clip	auto	ges_layer_remove_clip	Result<(), glib::BoolError>	Returns TRUE if the clip could be removed, FALSE if the layer does not want to remove the clip.
Pipeline.set_timeline	auto	ges_pipeline_set_timeline	Result<(), glib::BoolError>	Returns TRUE if the timeline could be successfully set on the pipeline , else FALSE.
Project.add_asset	auto	ges_project_add_asset	keep bool	Returns TRUE if the asset could be added FALSE it was already in the project. Note: FALSE is not an error but an indication
Project.add_encoding_profile	auto	ges_project_add_encoding_profile	Result<(), glib::BoolError>	Returns TRUE if profile could be added, FALSE otherwise
Project.create_asset	auto	ges_project_create_asset	keep bool	Returns TRUE if the asset started to be added FALSE it was already in the project. Note: FALSE is not an error but an indication
Project.remove_asset	auto	ges_project_remove_asset	Result<(), glib::BoolError>	Returns TRUE if the asset could be removed FALSE otherwise
Timeline.commit	auto	ges_timeline_commit	keep bool	Returns TRUE if pending changes were commited or FALSE if nothing needed to be commited. This means that if FALSE is returned then no "commited" signal will be emited. Note: FALSE is not an error but an indication
Timeline.commit_sync	auto	ges_timeline_commit_sync	keep bool	Returns TRUE if pending changes were commited or FALSE if nothing needed to be commited. Note: FALSE is not an error but an indication
Timeline.get_auto_transition	auto	ges_timeline_get_auto_transition	keep bool	Returns TRUE if transitions are automatically added, else FALSE. Note: returned value is a genuine boolean
Timeline.remove_track	auto	ges_timeline_remove_track	Result<(), glib::BoolError>	Returns TRUE if the track was properly removed, else FALSE.
TimelineElement.ripple	auto	ges_timeline_element_ripple	Result<(), glib::BoolError>	Returns TRUE if the self as been rippled properly, FALSE if an error occured
TimelineElement.ripple_end	auto	ges_timeline_element_ripple_end	Result<(), glib::BoolError>	Returns TRUE if the self as been rippled properly, FALSE if an error occured
TimelineElement.roll_end	auto	ges_timeline_element_roll_end	Result<(), glib::BoolError>	Returns TRUE if the self as been rolled properly, FALSE if an error occured
TimelineElement.roll_start	auto	ges_timeline_element_roll_start	Result<(), glib::BoolError>	Returns TRUE if the self as been roll properly, FALSE if an error occured
TimelineElement.set_name	auto	ges_timeline_element_set_name	Result<(), glib::BoolError>	No doc
TimelineElement.set_parent	auto	ges_timeline_element_set_parent	Result<(), glib::BoolError>	Returns TRUE if parent could be set or FALSE when self already had a parent or self and parent are the same.
TimelineElement.set_timeline	auto	ges_timeline_element_set_timeline	Result<(), glib::BoolError>	Returns TRUE if timeline could be set or FALSE when timeline already had a timeline.
TimelineElement.trim	auto	ges_timeline_element_trim	Result<(), glib::BoolError>	Returns TRUE if the self as been trimmed properly, FALSE if an error occured
Track.commit	auto	ges_track_commit	keep bool	Returns TRUE if something as been commited FALSE if nothing needed to be commited. Note: FALSE is not an error but an indication
Track.get_mixing	auto	ges_track_get_mixing	keep bool	Returns True if there is a mixer, False otherwise. Note: returned value is a genuine boolean
TrackElement.edit	auto	ges_track_element_edit	Result<(), glib::BoolError>	Returns TRUE if the object as been edited properly, FALSE if an error occured
TrackElement.remove_control_binding	auto	ges_track_element_remove_control_binding	Result<(), glib::BoolError>	Returns TRUE if the binding could be removed, FALSE if an error occured
TrackElement.set_active	auto	ges_track_element_set_active	keep bool	Returns TRUE if the property was toggled, else FALSE. Note: FALSE is not an error but an indication