[clang-tidy] Call StringMap::find without constructing std::string (NFC) (#115114)

StringMap::find takes StringRef, so we don't need to allocate
temporary instances of std::string.

Author: kazutakahirata

clang-tools-extra/clang-tidy/abseil/DurationRewriter.cpp

@@ -244,7 +244,7 @@ std::optional<DurationScale> getScaleForDurationInverse(llvm::StringRef Name) {
        {"ToDoubleNanoseconds", DurationScale::Nanoseconds},
        {"ToInt64Nanoseconds", DurationScale::Nanoseconds}});
 
-  auto ScaleIter = ScaleMap.find(std::string(Name));
+  auto ScaleIter = ScaleMap.find(Name);
   if (ScaleIter == ScaleMap.end())
     return std::nullopt;
 
@@ -260,7 +260,7 @@ std::optional<DurationScale> getScaleForTimeInverse(llvm::StringRef Name) {
        {"ToUnixMicros", DurationScale::Microseconds},
        {"ToUnixNanos", DurationScale::Nanoseconds}});
 
-  auto ScaleIter = ScaleMap.find(std::string(Name));
+  auto ScaleIter = ScaleMap.find(Name);
   if (ScaleIter == ScaleMap.end())
     return std::nullopt;