AK+LibJS: Extract some UTF-16 helpers for use in an outside class

An upcoming Utf16String will need access to these helpers. Let's make
them publicly available.

Libraries/LibJS/Parser.cpp

@@ -9,13 +9,14 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include "Parser.h"
 #include <AK/Array.h>
 #include <AK/CharacterTypes.h>
 #include <AK/HashTable.h>
 #include <AK/ScopeGuard.h>
 #include <AK/StdLibExtras.h>
 #include <AK/TemporaryChange.h>
+#include <AK/UnicodeUtils.h>
+#include <LibJS/Parser.h>
 #include <LibJS/Runtime/RegExpObject.h>
 #include <LibRegex/Regex.h>
 
@@ -4601,7 +4602,7 @@ FlyString Parser::consume_string_value()
     Utf8View view { value.bytes_as_string_view().substring_view(value.bytes().size() - 3) };
     VERIFY(view.length() <= 3);
     auto codepoint = *view.begin();
-    if (Utf16View::is_high_surrogate(codepoint)) {
+    if (AK::UnicodeUtils::is_utf16_high_surrogate(codepoint)) {
         syntax_error("StringValue ending with unpaired high surrogate"_string);
         VERIFY(view.length() == 1);
     }

Libraries/LibJS/Runtime/PrimitiveString.cpp

@@ -8,6 +8,7 @@
 #include <AK/CharacterTypes.h>
 #include <AK/FlyString.h>
 #include <AK/StringBuilder.h>
+#include <AK/UnicodeUtils.h>
 #include <AK/Utf16View.h>
 #include <AK/Utf8View.h>
 #include <LibJS/Runtime/AbstractOperations.h>
@@ -308,7 +309,7 @@ void RopeString::resolve(EncodingPreference preference) const
         auto high_surrogate = *Utf8View(previous_string_as_utf8.substring_view(previous_string_as_utf8.length() - 3)).begin();
         auto low_surrogate = *Utf8View(current_string_as_utf8).begin();
 
-        if (!Utf16View::is_high_surrogate(high_surrogate) || !Utf16View::is_low_surrogate(low_surrogate)) {
+        if (!AK::UnicodeUtils::is_utf16_high_surrogate(high_surrogate) || !AK::UnicodeUtils::is_utf16_low_surrogate(low_surrogate)) {
             builder.append(current_string_as_utf8);
             previous = current;
             continue;
@@ -316,7 +317,7 @@ void RopeString::resolve(EncodingPreference preference) const
 
         // Remove 3 bytes from the builder and replace them with the UTF-8 encoded code point.
         builder.trim(3);
-        builder.append_code_point(Utf16View::decode_surrogate_pair(high_surrogate, low_surrogate));
+        builder.append_code_point(AK::UnicodeUtils::decode_utf16_surrogate_pair(high_surrogate, low_surrogate));
 
         // Append the remaining part of the current string.
         builder.append(current_string_as_utf8.substring_view(3));

Libraries/LibJS/Runtime/StringConstructor.cpp

@@ -5,8 +5,8 @@
  */
 
 #include <AK/StringBuilder.h>
+#include <AK/UnicodeUtils.h>
 #include <AK/Utf16View.h>
-#include <AK/Utf32View.h>
 #include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/Error.h>
@@ -129,7 +129,9 @@ JS_DEFINE_NATIVE_FUNCTION(StringConstructor::from_code_point)
             return vm.throw_completion<RangeError>(ErrorType::InvalidCodePoint, next_code_point.to_string_without_side_effects());
 
         // d. Set result to the string-concatenation of result and UTF16EncodeCodePoint(ℝ(nextCP)).
-        MUST(code_point_to_utf16(string, static_cast<u32>(code_point)));
+        (void)AK::UnicodeUtils::code_point_to_utf16(static_cast<u32>(code_point), [&](auto code_unit) {
+            string.append(code_unit);
+        });
     }
 
     // 3. Assert: If codePoints is empty, then result is the empty String.

Libraries/LibJS/Runtime/StringPrototype.cpp

@@ -8,6 +8,7 @@
 #include <AK/Checked.h>
 #include <AK/Function.h>
 #include <AK/StringBuilder.h>
+#include <AK/UnicodeUtils.h>
 #include <AK/Utf16View.h>
 #include <LibGC/Heap.h>
 #include <LibJS/Runtime/AbstractOperations.h>
@@ -121,7 +122,7 @@ CodePoint code_point_at(Utf16View const& string, size_t position)
     }
 
     // 6. If first is a trailing surrogate or position + 1 = size, then
-    if (Utf16View::is_low_surrogate(first) || (position + 1 == string.length_in_code_units())) {
+    if (AK::UnicodeUtils::is_utf16_low_surrogate(first) || (position + 1 == string.length_in_code_units())) {
         // a. Return the Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]: true }.
         return { true, code_point, 1 };
     }
@@ -130,13 +131,13 @@ CodePoint code_point_at(Utf16View const& string, size_t position)
     auto second = string.code_unit_at(position + 1);
 
     // 8. If second is not a trailing surrogate, then
-    if (!Utf16View::is_low_surrogate(second)) {
+    if (!AK::UnicodeUtils::is_utf16_low_surrogate(second)) {
         // a. Return the Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]: true }.
         return { true, code_point, 1 };
     }
 
     // 9. Set cp to UTF16SurrogatePairToCodePoint(first, second).
-    code_point = Utf16View::decode_surrogate_pair(first, second);
+    code_point = AK::UnicodeUtils::decode_utf16_surrogate_pair(first, second);
 
     // 10. Return the Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 2, [[IsUnpairedSurrogate]]: false }.
     return { false, code_point, 2 };