there is no effect when I map "C-【" to ESC

Describe the bug
when I add

 "vim.insertModeKeyBindings": [
        {
            "before": ["<C-【>"],
            "after": ["<Esc>"]
        }
    ]

to setting file。there is no effect when I press C-【
the "【" is a character when I use Chinese input method in mac.
To Reproduce
Steps to reproduce the behavior:

add

 "vim.insertModeKeyBindings": [
        {
            "before": ["<C-【>"],
            "after": ["<Esc>"]
        }
    ]

to setting file

Expected behavior
I hope

 "vim.insertModeKeyBindings": [
        {
            "before": ["<C-【>"],
            "after": ["<Esc>"]
        }
    ]

have same effect with

 "vim.insertModeKeyBindings": [
        {
            "before": ["<C-[>"],
            "after": ["<Esc>"]
        }
    ]

• Extension (VsCodeVim) version: v1.13.1
• VSCode version:
• OS:

Version: 1.43.2
Commit: 0ba0ca52957102ca3527cf479571617f0de6ed50
Date: 2020-03-24T07:34:57.037Z
Electron: 7.1.11
Chrome: 78.0.3904.130
Node.js: 12.8.1
V8: 7.8.279.23-electron.0
OS: Darwin x64 19.4.0

Start by reproducing the vim.insertModeKeyBindings example on macOS with a Chinese input method, comparing "C-【" with "C-[" in the VSCodeVim extension. Trace the keybinding and input-event handling entry point, then verify that both mappings produce the expected Escape behavior.