subscriber: rename Layer::new_span to on_new_span (#1674)

While we're breaking things, we may as well do this as well.

Closes #630
Closes #662

Author: hawkw

tracing-opentelemetry/benches/trace.rs

@@ -60,7 +60,7 @@ impl<S> tracing_subscriber::Layer<S> for RegistryAccessLayer
 where
     S: tracing_core::Subscriber + for<'span> tracing_subscriber::registry::LookupSpan<'span>,
 {
-    fn new_span(
+    fn on_new_span(
         &self,
         _attrs: &tracing_core::span::Attributes<'_>,
         id: &tracing::span::Id,
@@ -87,7 +87,7 @@ impl<S> tracing_subscriber::Layer<S> for OtelDataLayer
 where
     S: tracing_core::Subscriber + for<'span> tracing_subscriber::registry::LookupSpan<'span>,
 {
-    fn new_span(
+    fn on_new_span(
         &self,
         attrs: &tracing_core::span::Attributes<'_>,
         id: &tracing::span::Id,

tracing-opentelemetry/src/layer.rs

@@ -410,7 +410,7 @@ where
     ///
     /// [OpenTelemetry `Span`]: opentelemetry::trace::Span
     /// [tracing `Span`]: tracing::Span
-    fn new_span(&self, attrs: &Attributes<'_>, id: &span::Id, ctx: Context<'_, S>) {
+    fn on_new_span(&self, attrs: &Attributes<'_>, id: &span::Id, ctx: Context<'_, S>) {
         let span = ctx.span(id).expect("Span not found, this is a bug");
         let mut extensions = span.extensions_mut();