Add a FileWriter interface (#7821)

* Add a FileWriter interface

* Change interface

* Provide 2 impl for File interface: FileManager & FileNameManager

* Update

* update

* Update

* Add file_writer file

* Update

* Format files

* Update based on review

* Update

* Format bzl file

* Add LoadFile function

* Format

---------

Co-authored-by: Derek Bailey <derekbailey@google.com>

include/flatbuffers/flatbuffer_builder.h

@@ -1184,7 +1184,8 @@ class FlatBufferBuilder {
   // Allocates space for a vector of structures.
   // Must be completed with EndVectorOfStructs().
   template<typename T> T *StartVectorOfStructs(size_t vector_size) {
-    StartVector(vector_size * sizeof(T) / AlignOf<T>(), sizeof(T), AlignOf<T>());
+    StartVector(vector_size * sizeof(T) / AlignOf<T>(), sizeof(T),
+                AlignOf<T>());
     return reinterpret_cast<T *>(buf_.make_space(vector_size * sizeof(T)));
   }