Abstracting away flatcc from any users of etdump (#1376)

Summary:
Pull Request resolved: #1376

This diff hides away all the flatcc types and isolates them `etdump_flatcc.cpp` so that any user who includes `etdump_flatcc.h` doesn't need to access any of the flatcc namespace variables.

Most of these issues surfaced while integrating etdump into coreml_executor_runner.

Reviewed By: Jack-Khuu

Differential Revision: D51966334

fbshipit-source-id: 7b89c39a8ac41272fbcaa8ece70ec3863c6c0136

Author: tarun292

sdk/etdump/emitter.h

@@ -9,43 +9,14 @@
 #include <stdint.h>
 #include <stdlib.h>
 
+#include <executorch/sdk/etdump/etdump_flatcc.h>
 #include <flatcc/flatcc_builder.h>
 
 #pragma once
 
 namespace torch {
 namespace executor {
 
-struct etdump_static_allocator {
-  etdump_static_allocator(
-      uint8_t* buffer,
-      size_t total_buf_size,
-      size_t alloc_buf_size)
-      : data{buffer},
-        data_size{alloc_buf_size},
-        allocated{0},
-        out_size{total_buf_size - alloc_buf_size},
-        front_cursor{&buffer[alloc_buf_size]},
-        front_left{out_size / 2} {}
-  // Pointer to backing buffer to allocate from.
-  uint8_t* data{nullptr};
-
-  // Size of backing buffer.
-  size_t data_size{0};
-
-  // Current allocation offset.
-  size_t allocated{0};
-
-  // Size of build buffer.
-  size_t out_size{0};
-
-  // Pointer to front of build buffer.
-  uint8_t* front_cursor{nullptr};
-
-  // Bytes left in front of front_cursor.
-  size_t front_left{0};
-};
-
 int et_flatcc_custom_init(
     flatcc_builder_t* builder,
     struct etdump_static_allocator* alloc);