add fileSize() method to Dir object

cores/esp8266/FS.cpp

@@ -144,6 +144,14 @@ String Dir::fileName() {
     return _impl->fileName();
 }
 
+size_t Dir::fileSize() {
+    if (!_impl) {
+        return 0;
+    }
+
+    return _impl->fileSize();
+}
+
 bool Dir::next() {
     if (!_impl) {
         return false;

cores/esp8266/FS.h

@@ -78,6 +78,7 @@ public:
 
     File openFile(const char* mode);
     String fileName();
+    size_t fileSize();
     bool next();
 
 protected:

cores/esp8266/FSImpl.h

@@ -56,6 +56,7 @@ public:
     virtual ~DirImpl() { }
     virtual FileImplPtr openFile(OpenMode openMode, AccessMode accessMode) = 0;
     virtual const char* fileName() = 0;
+    virtual size_t fileSize() = 0;
     virtual bool next() = 0;
 };
 

cores/esp8266/spiffs_api.cpp

@@ -308,6 +308,13 @@ public:
         return (const char*) _dirent.name;
     }
 
+    size_t fileSize() override {
+        if (!_valid)
+            return 0;
+
+        return _dirent.size;
+    }
+
     bool next() override {
         spiffs_dirent* result = SPIFFS_readdir(&_dir, &_dirent);
         _valid = (result != nullptr);