lib/icu/CaseFold: rename to IcuCanonicalize() and add flag parameter

Prepare for adding more transformations.

src/lib/icu/Canonicalize.hxx

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2003-2022 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#pragma once
+
+#include "config.h"
+
+#ifdef HAVE_ICU
+#define HAVE_ICU_CANONICALIZE
+
+#include <string_view>
+
+class AllocatedString;
+
+/**
+ * Transform the given string to "canonical" form to allow fuzzy
+ * string comparisons.  The full set of features (if ICU is being
+ * used):
+ *
+ * - case folding (optional)
+ */
+AllocatedString
+IcuCanonicalize(std::string_view src, bool fold_case) noexcept;
+
+#endif