Pasting an emoji in code creates an invisible error (Parse Error: Unknown character)

[GuyUnger]

Godot version:
3.1 beta 3

OS/device including version:
Windows 10

Issue description:
When you paste an emoji in the code editor, it looks like it didn't accept the symbol because no character is shown. But it's there so it throws an unkown character error. It won't happen to people often but if it does happen, it could keep people clueless of what the problem is because you don't see anything wrong.

Steps to reproduce:
Paste an emoji in the code editor

[bruvzg]

Related to #23093, on Windows Godot uses 16-bit char type and does not support surrogate pairs (characters with codes > 0xFFFF won't work).

[girng]

i think godot is trying to tell us something

[GuyUnger]

Yeah the code doesn't need support for emojis imo, but the code should either not accept the character at all or show a "missing symbol" symbol

[bruvzg]

or show a "missing symbol" symbol

Missing char symbol is shown in other input fields (using Noto Sans UI font) but not in the code editor (using Hack font), that's probably a problem with the font.

[KoBeWi]

Still valid in 05395cb