LibLocale: Move locale source files to the LibLocale folder

These are still included in LibUnicode, but this updates their location
and the include paths of other files which include them.

Userland/Libraries/LibLocale/PluralRules.h

@@ -0,0 +1,124 @@
+/*
+ * Copyright (c) 2022, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Assertions.h>
+#include <AK/StringView.h>
+#include <AK/Types.h>
+#include <LibLocale/Forward.h>
+
+namespace Locale {
+
+enum class PluralForm {
+    Cardinal,
+    Ordinal,
+};
+
+enum class PluralCategory : u8 {
+    Other,
+    Zero,
+    One,
+    Two,
+    Few,
+    Many,
+
+    // https://unicode.org/reports/tr35/tr35-numbers.html#Explicit_0_1_rules
+    ExactlyZero,
+    ExactlyOne,
+};
+
+// https://unicode.org/reports/tr35/tr35-numbers.html#Plural_Operand_Meanings
+struct PluralOperands {
+    static constexpr StringView symbol_to_variable_name(char symbol)
+    {
+        if (symbol == 'n')
+            return "number"sv;
+        if (symbol == 'i')
+            return "integer_digits"sv;
+        if (symbol == 'f')
+            return "fraction_digits"sv;
+        if (symbol == 'v')
+            return "number_of_fraction_digits"sv;
+        if (symbol == 't')
+            return "fraction_digits_without_trailing"sv;
+        if (symbol == 'w')
+            return "number_of_fraction_digits_without_trailing"sv;
+        VERIFY_NOT_REACHED();
+    }
+
+    static constexpr bool symbol_requires_floating_point_modulus(char symbol)
+    {
+        // From TR-35: "The modulus (% or mod) is a remainder operation as defined in Java; for
+        // example, where n = 4.3 the result of n mod 3 is 1.3."
+        //
+        // So, this returns whether the symbol represents a decimal value, and thus requires fmod.
+        return symbol == 'n';
+    }
+
+    double number { 0 };
+    u64 integer_digits { 0 };
+    u64 fraction_digits { 0 };
+    u64 number_of_fraction_digits { 0 };
+    u64 fraction_digits_without_trailing { 0 };
+    u64 number_of_fraction_digits_without_trailing { 0 };
+};
+
+PluralForm plural_form_from_string(StringView plural_form);
+StringView plural_form_to_string(PluralForm plural_form);
+
+// NOTE: This must be defined inline to be callable from the code generators.
+constexpr PluralCategory plural_category_from_string(StringView category)
+{
+    if (category == "other"sv)
+        return PluralCategory::Other;
+    if (category == "zero"sv)
+        return PluralCategory::Zero;
+    if (category == "one"sv)
+        return PluralCategory::One;
+    if (category == "two"sv)
+        return PluralCategory::Two;
+    if (category == "few"sv)
+        return PluralCategory::Few;
+    if (category == "many"sv)
+        return PluralCategory::Many;
+    if (category == "0"sv)
+        return PluralCategory::ExactlyZero;
+    if (category == "1"sv)
+        return PluralCategory::ExactlyOne;
+    VERIFY_NOT_REACHED();
+}
+
+// NOTE: This must be defined inline to be callable from the code generators.
+constexpr StringView plural_category_to_string(PluralCategory category)
+{
+    switch (category) {
+    case PluralCategory::Other:
+        return "other"sv;
+    case PluralCategory::Zero:
+        return "zero"sv;
+    case PluralCategory::One:
+        return "one"sv;
+    case PluralCategory::Two:
+        return "two"sv;
+    case PluralCategory::Few:
+        return "few"sv;
+    case PluralCategory::Many:
+        return "many"sv;
+    case PluralCategory::ExactlyZero:
+        return "0"sv;
+    case PluralCategory::ExactlyOne:
+        return "1"sv;
+    }
+
+    VERIFY_NOT_REACHED();
+}
+
+PluralCategory determine_plural_category(StringView locale, PluralForm form, PluralOperands operands);
+Span<PluralCategory const> available_plural_categories(StringView locale, PluralForm form);
+PluralCategory determine_plural_range(StringView locale, PluralCategory start, PluralCategory end);
+
+}