LibJS+LibUnicode: Implement retrieval of collator keyword values

Completely missed this when implementing Intl.Collator!

Libraries/LibJS/Tests/builtins/Intl/Collator/Collator.prototype.resolvedOptions.js

@@ -54,12 +54,21 @@ describe("correct behavior", () => {
     });
 
     test("collation", () => {
-        // Only "default" collation is parsed for now.
-        const en = new Intl.Collator("en");
-        expect(en.resolvedOptions().collation).toBe("default");
+        const en1 = new Intl.Collator("en");
+        expect(en1.resolvedOptions().locale).toBe("en");
+        expect(en1.resolvedOptions().collation).toBe("default");
+
+        const en2 = new Intl.Collator("en-u-co-phonebk", { collation: "pinyin" });
+        expect(en2.resolvedOptions().locale).toBe("en");
+        expect(en2.resolvedOptions().collation).toBe("default");
 
         const el = new Intl.Collator("el", { collation: "foo" });
+        expect(el.resolvedOptions().locale).toBe("el");
         expect(el.resolvedOptions().collation).toBe("default");
+
+        const de = new Intl.Collator("de-u-co-phonebk", { collation: "pinyin" });
+        expect(de.resolvedOptions().locale).toBe("de-u-co-phonebk");
+        expect(de.resolvedOptions().collation).toBe("phonebk");
     });
 
     test("numeric may be set by locale extension", () => {

Libraries/LibJS/Tests/builtins/Intl/Intl.supportedValuesOf.js

@@ -26,7 +26,7 @@ describe("normal behavior", () => {
         const values = Intl.supportedValuesOf("collation");
         expect(isSorted(values)).toBeTrue();
 
-        expect(values.indexOf("default")).not.toBe(-1);
+        expect(values.indexOf("emoji")).not.toBe(-1);
     });
 
     test("currency", () => {

Libraries/LibUnicode/UnicodeKeywords.cpp

@@ -110,15 +110,48 @@ Vector<String> const& available_collation_numeric_orderings()
 
 Vector<String> const& available_collations()
 {
-    // FIXME: Implement this when we fully support Intl.Collator.
-    static Vector<String> collations { "default"_string };
+    static auto collations = []() -> Vector<String> {
+        UErrorCode status = U_ZERO_ERROR;
+
+        auto keywords = adopt_own_if_nonnull(icu::Collator::getKeywordValues("collation", status));
+        if (icu_failure(status))
+            return {};
+
+        auto collations = icu_string_enumeration_to_list(move(keywords), "co", [](char const* value, size_t value_length) {
+            // https://tc39.es/ecma402/#sec-properties-of-intl-collator-instances
+            // the values "standard" and "search" are not allowed
+            return !StringView { value, value_length }.is_one_of("standard"sv, "search"sv);
+        });
+
+        quick_sort(collations);
+        return collations;
+    }();
+
     return collations;
 }
 
-Vector<String> available_collations(StringView)
+Vector<String> available_collations(StringView locale)
 {
-    // FIXME: Implement this when we fully support Intl.Collator.
-    return available_collations();
+    UErrorCode status = U_ZERO_ERROR;
+
+    auto locale_data = LocaleData::for_locale(locale);
+    if (!locale_data.has_value())
+        return {};
+
+    auto keywords = adopt_own_if_nonnull(icu::Collator::getKeywordValuesForLocale("collation", locale_data->locale(), true, status));
+    if (icu_failure(status))
+        return {};
+
+    auto collations = icu_string_enumeration_to_list(move(keywords), "co", [](char const* value, size_t value_length) {
+        // https://tc39.es/ecma402/#sec-properties-of-intl-collator-instances
+        // the values "standard" and "search" are not allowed
+        return !StringView { value, value_length }.is_one_of("standard"sv, "search"sv);
+    });
+
+    if (!collations.contains_slow("default"sv))
+        collations.prepend("default"_string);
+
+    return collations;
 }
 
 Vector<String> const& available_hour_cycles()