Android virtual keyboard doesn't respect max length of LineEdit

[KoBeWi]

Godot version:
3.2 alpha

OS/device including version:
Android 7 on Xiaomi Redmi Note 4

Issue description:
When you set a maximum length for LineEdit, it works alright on desktop, but on Android you can write past the limit. It won't appear in the LineEdit, but the extra letters will show on virtual keyboard.

What's worse, doing "Backspace" has no effect in LineEdit until you remove all the extra letters.

Minimal reproduction project:
ReproductionProject.zip

[MadEqua]

Is iOS behaving differently?

I can fix this on Android this by adding a max_input_length parameter to OS::show_virtual_keyboard()

godot/core/os/os.h

Line 383 in 4b31231

virtual void show_virtual_keyboard(const String &p_existing_text, const Rect2 &p_screen_rect = Rect2());

passing it into Java land to an InputFilter used when requesting a keyboard. This should stop the soft keyboard apps to accept any number of characters.

Other implementations of OS::show_virtual_keyboard() (iOS and UWP, I think) will just ignore the new parameter.