gstreamer: Move various MetaAPI methods to an extension trait

These don't make sense to implement any different than the default.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/-/merge_requests/1284>

gstreamer/src/lib.rs

@@ -104,7 +104,8 @@ pub mod meta;
 #[cfg_attr(docsrs, doc(cfg(feature = "v1_16")))]
 pub use crate::meta::MetaSeqnum;
 pub use crate::meta::{
-    Meta, MetaAPI, MetaRef, MetaRefMut, ParentBufferMeta, ProtectionMeta, ReferenceTimestampMeta,
+    Meta, MetaAPI, MetaAPIExt, MetaRef, MetaRefMut, ParentBufferMeta, ProtectionMeta,
+    ReferenceTimestampMeta,
 };
 pub mod buffer;
 pub use crate::buffer::{
@@ -322,7 +323,7 @@ pub mod prelude {
         gobject::GObjectExtManualGst,
         memory::MemoryType,
         message::MessageErrorDomain,
-        meta::MetaAPI,
+        meta::{MetaAPI, MetaAPIExt},
         miniobject::IsMiniObject,
         object::GstObjectExtManual,
         pad::PadExtManual,

gstreamer/src/meta.rs

@@ -14,7 +14,23 @@ pub unsafe trait MetaAPI: Sync + Send + Sized {
 
     #[doc(alias = "get_meta_api")]
     fn meta_api() -> glib::Type;
+}
 
+pub trait MetaAPIExt: MetaAPI {
+    #[doc(alias = "gst_meta_api_type_has_tag")]
+    fn has_tag(&self, tag: glib::Quark) -> bool;
+
+    #[doc(alias = "gst_meta_api_type_get_tags")]
+    fn tags(&self) -> &[glib::GStringPtr];
+
+    unsafe fn from_ptr(buffer: &BufferRef, ptr: *const Self::GstType) -> MetaRef<Self>;
+    unsafe fn from_mut_ptr<T>(
+        buffer: &mut BufferRef,
+        ptr: *mut Self::GstType,
+    ) -> MetaRefMut<Self, T>;
+}
+
+impl<A: MetaAPI> MetaAPIExt for A {
     fn has_tag(&self, tag: glib::Quark) -> bool {
         unsafe {
             from_glib(ffi::gst_meta_api_type_has_tag(