subscriber: Move the default EnvFilter to CollectorBuilder

This resolves the disparity between fmt::init() and fmt().init().

Unfortunately, this involves a change to type signature and therefore
is a breaking change.

Close tokio-rs#1329

tracing-subscriber/src/fmt/mod.rs

@@ -472,8 +472,14 @@ impl Collector {
     pub const DEFAULT_MAX_LEVEL: LevelFilter = LevelFilter::INFO;
 
     /// Returns a new `CollectorBuilder` for configuring a format subscriber.
-    pub fn builder() -> CollectorBuilder {
-        CollectorBuilder::default()
+    pub fn builder() -> CollectorBuilder<format::DefaultFields,
+        format::Format, impl subscribe::Subscribe<Formatter> + Send + Sync + 'static> {
+        let builder = CollectorBuilder::default();
+
+        #[cfg(feature = "env-filter")]
+        let builder = builder.with_env_filter(crate::EnvFilter::from_default_env());
+
+        builder
     }
 
     /// Returns a new format subscriber with the default configuration.
@@ -1167,10 +1173,6 @@ impl<N, E, F, W> CollectorBuilder<N, E, F, W> {
 ///     ../filter/struct.EnvFilter.html#associatedconstant.DEFAULT_ENV
 pub fn try_init() -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
     let builder = Collector::builder();
-
-    #[cfg(feature = "env-filter")]
-    let builder = builder.with_env_filter(crate::EnvFilter::from_default_env());
-
     builder.try_init()
 }