LibUnicode: Add decomposition mappings and Unicode normalization

The mappings are exposed via `Unicode::code_point_decomposition(u32)`
and `Unicode::code_point_decompositions()`, the latter being useful for
reverse searching a code point from its decomposition.

The normalization code does not make use of `Quick_Check` props (https://www.unicode.org/reports/tr44/#Decompositions_and_Normalization),
meaning no quick check optimizations.

Userland/Libraries/LibUnicode/Normalize.h

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2022, mat
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Forward.h>
+#include <AK/Optional.h>
+#include <AK/Span.h>
+#include <AK/String.h>
+#include <AK/StringView.h>
+#include <LibUnicode/Forward.h>
+
+namespace Unicode {
+
+Optional<CodePointDecomposition const&> code_point_decomposition(u32 code_point);
+Span<CodePointDecomposition const> code_point_decompositions();
+
+enum class NormalizationForm {
+    NFD,
+    NFC,
+    NFKD,
+    NFKC
+};
+
+[[nodiscard]] String normalize(StringView string, NormalizationForm form);
+
+}