GtkColorButton: Use G_PARAM_EXPLICIT_NOTIFY
GtkColorChooser: Use G_PARAM_EXPLICIT_NOTIFY for use-alpha

Implementors will need to adjust.
GtkColorChooserDialog: Explicitly notify for use-alpha
GtkColorChooserWidget: Explicitly notify for use-alpha
GtkEntry: Don't forget to notify for the tooltip markup props
GtkEntry: Explicitly notify for populate-all
GtkEntryBuffer: Use G_PARAM_EXPLICIT_NOTIFY

Also avoid redundant notification for max-length.
GtkEntryCompletion: Use G_PARAM_EXPLICIT_NOTIFY

Also, use the setter for text-column, internally.
GtkFrame: Use G_PARAM_EXPLICIT_NOTIFY
GtkMenuItem: Use G_PARAM_EXPLICIT_NOTIFY
GtkToggleButton: Use G_PARAM_EXPLICIT_NOTIFY
GtkEventBox: Use G_PARAM_EXPLICIT_NOTIFY
GtkExpander: Use G_PARAM_EXPLICIT_NOTIFY
GtkFlowBox: Explicitly notify orientation
GtkFontChooser: Use G_PARAM_EXPLICIT_NOTIFY for show-preview-entry

Implementors will have to be adjusted.
GtkFontButton: Fix the handling of show-preview-button

We were not storing the value at all, and not notifying.
GtkFontButton Trivial cleanup

Replace GTK_PARAM_READABLE|GTK_PARAM_WRITABLE by GTK_PARAM_READWRITE.
GtkFontButton: Use G_PARAM_EXPLICIT_NOTIFY
GtkEventController: Use G_PARAM_EXPLICIT_NOTIFY
GdkOffscreenWindow: Fill in a few more vfuncs

Mostly to avoid special cases in testcases.