Make all file access 64-bit (uint64_t)

This changes the types of a big number of variables.

General rules:
- Using `uint64_t` in general. We also considered `int64_t` but eventually
  settled on keeping it unsigned, which is also closer to what one would expect
  with `size_t`/`off_t`.
- We only keep `int64_t` for `seek_end` (takes a negative offset from the end)
  and for the `Variant` bindings, since `Variant::INT` is `int64_t`. This means
  we only need to guard against passing negative values in `core_bind.cpp`.
- Using `uint32_t` integers for concepts not needing such a huge range, like
  pages, blocks, etc.

In addition:
- Improve usage of integer types in some related places; namely, `DirAccess`,
  core binds.

Note:
- On Windows, `_ftelli64` reports invalid values when using 32-bit MinGW with
  version < 8.0. This was an upstream bug fixed in 8.0. It breaks support for
  big files on 32-bit Windows builds made with that toolchain. We might add a
  workaround.

Fixes #44363.
Fixes godotengine/godot-proposals#400.

Co-authored-by: Rémi Verschelde <rverschelde@gmail.com>

core/io/resource_format_binary.cpp

@@ -1106,8 +1106,8 @@ Error ResourceFormatLoaderBinary::rename_dependencies(const String &p_path, cons
 
 	save_ustring(fw, get_ustring(f)); //type
 
-	size_t md_ofs = f->get_position();
-	size_t importmd_ofs = f->get_64();
+	uint64_t md_ofs = f->get_position();
+	uint64_t importmd_ofs = f->get_64();
 	fw->store_64(0); //metadata offset
 
 	for (int i = 0; i < 14; i++) {