Use FxHashMap and FxHashSet in hot code paths

We can also use these maps and sets in place of `SeaHasher` because
they are also deterministic. Note that we're not swapping std's
`HashMap` and `HashSet` wholesale inside of `collections` because
on the server we need cryptographically secure collections.

crates/collections/Cargo.toml

@@ -9,7 +9,7 @@ path = "src/collections.rs"
 doctest = false
 
 [features]
-test-support = ["seahash"]
+test-support = []
 
 [dependencies]
-seahash = { version = "4.1", optional = true }
+rustc-hash = "1.1"

crates/collections/src/collections.rs

@@ -1,21 +1,8 @@
 #[cfg(feature = "test-support")]
-#[derive(Clone, Default)]
-pub struct DeterministicState;
+pub type HashMap<K, V> = FxHashMap<K, V>;
 
 #[cfg(feature = "test-support")]
-impl std::hash::BuildHasher for DeterministicState {
-    type Hasher = seahash::SeaHasher;
-
-    fn build_hasher(&self) -> Self::Hasher {
-        seahash::SeaHasher::new()
-    }
-}
-
-#[cfg(feature = "test-support")]
-pub type HashMap<K, V> = std::collections::HashMap<K, V, DeterministicState>;
-
-#[cfg(feature = "test-support")]
-pub type HashSet<T> = std::collections::HashSet<T, DeterministicState>;
+pub type HashSet<T> = FxHashSet<T>;
 
 #[cfg(not(feature = "test-support"))]
 pub type HashMap<K, V> = std::collections::HashMap<K, V>;
@@ -23,6 +10,7 @@ pub type HashMap<K, V> = std::collections::HashMap<K, V>;
 #[cfg(not(feature = "test-support"))]
 pub type HashSet<T> = std::collections::HashSet<T>;
 
+pub use rustc_hash::{FxHashMap, FxHashSet};
 use std::any::TypeId;
 pub use std::collections::*;