Fix string key issue with constexpr StrKey in Performance C++ native …

…module

Summary:
I encountered build error when using performance API in catalyst android mobile app. The error message P617433618 points at using non-const `std::strlen` API in a `constexpr`.

```
$ buck install catalyst-android
...
stderr: xplat/js/react-native-github/Libraries/WebPerformance/PerformanceEntryReporter.cpp:208:13: error: constexpr constructor never produces a constant expression [-Winvalid-constexpr]
  constexpr StrKey(const char *s)
            ^
xplat/js/react-native-github/Libraries/WebPerformance/PerformanceEntryReporter.cpp:209:39: note: non-constexpr function 'strlen' cannot be used in a constant expression
      : key(folly::hash::fnv32_buf(s, std::strlen(s))) {}
```

Changelog:
[General][Fixed] - Fixed string key calculation in constexpr from Performance C++ native module.

Reviewed By: javache

Differential Revision: D43136624

fbshipit-source-id: c691671b157b507745c67a505c91f75cf6b878d1

Libraries/WebPerformance/PerformanceEntryReporter.cpp

@@ -206,7 +206,7 @@ void PerformanceEntryReporter::scheduleFlushBuffer() {
 struct StrKey {
   uint32_t key;
   constexpr StrKey(const char *s)
-      : key(folly::hash::fnv32_buf(s, std::strlen(s))) {}
+      : key(folly::hash::fnv32_buf(s, sizeof(s) - 1)) {}
 
   constexpr bool operator==(const StrKey &rhs) const {
     return key == rhs.key;