Issue

In MOSH (https://mosh.mit.edu/) for exit I am need to input ctrl+^ (actually for this I am pressed keys ctrl, shift, 6).

In xterm.js this combination not worked.
In iTerm and native terminal app - this combination worked.

From MOSH manual:

ESCAPE SEQUENCES
       The  default  escape  character used by Mosh is ASCII RS (decimal 30).  
       This is typically typed as Ctrl-^ or Ctrl-Shift-6, on US English keyboards.  

In Chrome this combination succesfully catched by event keypress like this (key code === 30):

Details

• Browser and browser version: Google Chrome Version 80.0.3987.149 (Official Build) (64-bit)
• OS version: macOS 10.15.4
• xterm.js version: 4.4.0

Steps to reproduce

1. Show in xterm.js terminal from linux which have command showkey (I am use debian) and run

showkey -a

and then press ctrl, shift, 6 - nothing was happends.

2. In other terminal do same - and you will see: