[HTML5] Use 64KiB chunk size in JS HTTPClient.
[HTML5] Use 64KiB chunk size in JS HTTPClient.

For consistency with the native one, and the documentation.

(cherry picked from commit 6243835619b38134a78a98283ac9a350a990348e)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot