LibUnicode+Everywhere: Merge LibLocale back into LibUnicode

LibLocale was split off from LibUnicode a couple years ago to reduce the
number of applications on SerenityOS that depend on CLDR data. Now that
we use ICU, both LibUnicode and LibLocale are actually linking in this
data. And since vcpkg gives us static libraries, both libraries are over
30MB in size.

This patch reverts the separation and merges LibLocale into LibUnicode
again. We now have just one library that includes the ICU data.

Further, this will let LibUnicode share the locale cache that previously
would only exist in LibLocale.

Userland/Libraries/LibUnicode/RelativeTimeFormat.h

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2022-2024, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/NonnullOwnPtr.h>
+#include <AK/Optional.h>
+#include <AK/String.h>
+#include <AK/StringView.h>
+#include <AK/Vector.h>
+#include <LibUnicode/Forward.h>
+
+namespace Unicode {
+
+// These are just the subset of fields in the CLDR required for ECMA-402.
+enum class TimeUnit {
+    Second,
+    Minute,
+    Hour,
+    Day,
+    Week,
+    Month,
+    Quarter,
+    Year,
+};
+Optional<TimeUnit> time_unit_from_string(StringView);
+StringView time_unit_to_string(TimeUnit);
+
+enum class NumericDisplay {
+    Always,
+    Auto,
+};
+NumericDisplay numeric_display_from_string(StringView);
+StringView numeric_display_to_string(NumericDisplay);
+
+class RelativeTimeFormat {
+public:
+    static NonnullOwnPtr<RelativeTimeFormat> create(StringView locale, Style style);
+    virtual ~RelativeTimeFormat() = default;
+
+    struct Partition {
+        StringView type;
+        String value;
+        StringView unit;
+    };
+
+    virtual String format(double, TimeUnit, NumericDisplay) const = 0;
+    virtual Vector<Partition> format_to_parts(double, TimeUnit, NumericDisplay) const = 0;
+
+protected:
+    RelativeTimeFormat() = default;
+};
+
+}