Port sort key code from ICU4C (#2689)

components/collator/Cargo.toml

@@ -21,13 +21,14 @@ all-features = true
 [dependencies]
 displaydoc = { workspace = true }
 icu_collections = { workspace = true }
-icu_normalizer = { workspace = true }
+icu_normalizer = { workspace = true, features = ["utf8_iter", "utf16_iter"] }
 icu_locale_core = { workspace = true, features = ["alloc"] }
 icu_properties = { workspace = true }
 icu_provider = { workspace = true }
 utf8_iter = { workspace = true }
 utf16_iter = { workspace = true }
 smallvec = { workspace = true, features = ["union", "const_generics", "const_new"] } # alloc
+write16 = { workspace = true }
 zerovec = { workspace = true }
 
 databake = { workspace = true, optional = true, features = ["derive"] }