LibJS: Define Utf16String::to_utf8 to convert Utf16String to String

Userland/Libraries/LibJS/Runtime/Utf16String.cpp

@@ -102,6 +102,11 @@ Utf16View Utf16String::substring_view(size_t code_unit_offset) const
     return view().substring_view(code_unit_offset);
 }
 
+ThrowCompletionOr<String> Utf16String::to_utf8(VM& vm) const
+{
+    return TRY_OR_THROW_OOM(vm, view().to_utf8(Utf16View::AllowInvalidCodeUnits::Yes));
+}
+
 ThrowCompletionOr<DeprecatedString> Utf16String::to_deprecated_string(VM& vm) const
 {
     return TRY_OR_THROW_OOM(vm, view().to_deprecated_string(Utf16View::AllowInvalidCodeUnits::Yes));

Userland/Libraries/LibJS/Runtime/Utf16String.h

@@ -50,6 +50,7 @@ public:
     Utf16View substring_view(size_t code_unit_offset, size_t code_unit_length) const;
     Utf16View substring_view(size_t code_unit_offset) const;
 
+    ThrowCompletionOr<String> to_utf8(VM&) const;
     ThrowCompletionOr<DeprecatedString> to_deprecated_string(VM&) const;
     u16 code_unit_at(size_t index) const;