gstreamer: Simplify and speed up log message string construction

For pre-1.20 simply use `%s` as format string instead of escaping the
`%` inline while writing. This allows a simpler implementation and is
also faster, see https://github.com/gtk-rs/gtk-rs-core/pull/583.

gstreamer/src/log.rs

@@ -180,8 +180,6 @@ impl DebugCategory {
             None => ptr::null_mut(),
         };
 
-        #[cfg(feature = "v1_20")]
-        {
         let mut w = glib::GStringBuilder::default();
 
         // Can't really happen but better safe than sorry
@@ -189,6 +187,7 @@ impl DebugCategory {
             return;
         }
 
+        #[cfg(feature = "v1_20")]
         unsafe {
             ffi::gst_debug_log_literal(
                 cat.as_ptr(),
@@ -200,39 +199,7 @@ impl DebugCategory {
                 w.into_string().to_glib_none().0,
             );
         }
-        }
         #[cfg(not(feature = "v1_20"))]
-        {
-            // Replace literal percentage signs with two so that they are not interpreted as printf
-            // format specifiers
-            struct Write(glib::GStringBuilder);
-            impl fmt::Write for Write {
-                fn write_str(&mut self, mut s: &str) -> Result<(), fmt::Error> {
-                    while let Some((prefix, suffix)) = s.split_once('%') {
-                        self.0.append(prefix);
-                        self.0.append("%%");
-                        s = suffix;
-                    }
-                    self.0.append(s);
-                    Ok(())
-                }
-
-                fn write_char(&mut self, c: char) -> fmt::Result {
-                    if c == '%' {
-                        self.0.append("%%");
-                    } else {
-                        self.0.append_c(c);
-                    }
-                    Ok(())
-                }
-            }
-            let mut w = Write(glib::GStringBuilder::default());
-
-            // Can't really happen but better safe than sorry
-            if fmt::write(&mut w, args).is_err() {
-                return;
-            }
-
         unsafe {
             ffi::gst_debug_log(
                 cat.as_ptr(),
@@ -241,11 +208,11 @@ impl DebugCategory {
                 module.to_glib_none().0,
                 line as i32,
                 obj_ptr,
-                    w.0.into_string().to_glib_none().0,
+                b"%s\0".as_ptr() as *const _,
+                ToGlibPtr::<*const i8>::to_glib_none(&w.into_string()).0,
             );
         }
     }
-    }
 
     #[doc(alias = "get_all_categories")]
     #[doc(alias = "gst_debug_get_all_categories")]