Avoid copying string in parseNumberLiteral()

Author: catamorphism

Diff for: icu4c/source/i18n/messageformat2_function_registry.cpp

@@ -453,12 +453,10 @@ static double parseNumberLiteral(const FormattedPlaceholder& input, UErrorCode&
     using namespace double_conversion;
     int processedCharactersCount = 0;
     StringToDoubleConverter converter(0, 0, 0, "", "");
-    LocalArray<char> target(new char(len + 1));
-    int32_t bufferLen = inputStr.extract(0, len, target.getAlias());
-    U_ASSERT(bufferLen == len);
-    double result = converter.StringToDouble(target.getAlias(),
-                                             bufferLen,
-                                             &processedCharactersCount);
+    double result =
+        converter.StringToDouble(reinterpret_cast<const uint16_t*>(inputStr.getBuffer()),
+                                 len,
+                                 &processedCharactersCount);
     if (processedCharactersCount != len) {
         errorCode = U_MF_OPERAND_MISMATCH_ERROR;
     }