This allows `-Wswitch-enum` to catch unhandled properties in the `get_property()` and `set_property()` vfuncs. It doesn’t catch any bugs in practice at the moment, but is best practice. Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

This will marginally speed up class initialisation, as all the locks for adding pspecs to the `GObjectClass` will only have to be taken once, rather than N times. It also means we have a handy indexed `GParamSpec*` array ready to use in the following commit. Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

If these properties ever get names or descriptions added, this will avoid them being `strdup()`ed pointlessly by GObject. Since none of the properties currently have any strings set, this is currently a no-op. Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

This is best practice for GObjects, as it allows binding things together (particularly UI widgets) to update themselves when the properties of the object they represent are updated. In particular, this will eventually let us bind review property updates in gnome-software to the `GsReviewRow` widget so that it updates automatically when a review is upvoted/downvoted/etc. See https://gitlab.gnome.org/GNOME/gnome-software/-/merge_requests/1545. The `G_PARAM_EXPLICIT_NOTIFY` flag now needs to be passed to the pspecs so that `g_object_set_property()` doesn’t implicitly emit the `GObject::notify` signal when it’s called. That would result in a duplicate signal emission. Unfortunately we can’t rely on this implicit behaviour because C code is more likely to call `as_review_set_*()` directly, which doesn’t use the implicit behaviour. Hence `G_PARAM_EXPLICIT_NOTIFY`. Where possible, the `as_review_set_*()` methods have been changed to return early if the new value is the same as the old one, to avoid an unnecessary `GObject::notify` emission. Where functions from `as-utils.c` have been used, though, that’s not straightforward, so there is still currently an unnecessary signal emission. That’s not a great problem, as consumers of the signal must be able to accept spurious emissions of it. Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

This allows property change notifications for it, property bindings to it, and for it to be correctly exposed as a property in language bindings. Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

Commits on Nov 17, 2022