Feature: Shift Shift, Ctrl Ctrl, Alt Alt Keybinds (Double press modifer keybind support)

[PathToLife]

This PR fixes #5280 How to detect shift shift key in VSCode?

Proposed changes:

Implemented support for quick double presses of a modifier key without unit test regressions or noticeable performance hits, while following existing architecture as closely as possible.

This implementation improves UX experience for users migrating from JetBrains platform

Keybindings.json

    {
        "key": "shift shift",
        "command": "workbench.action.quickOpen"
    },
    {
        "key": "ctrl ctrl",
        "command": "workbench.action.showCommands"
    },
    {
        "key": "alt alt",
        "command": "workbench.action.quickOpen"
    },

• Implemented new keyboard event that checks for keyUp (critical for double press detection, second key MUST be released)
• Implemented additional keyup resolver for only modifiers, this will allow backwards compatibility with existing keybind system which uses keydown
• MacLinuxKeyboardMapper getDispatchString() had logic in places inconsistent with windowsKeyboardMapper, fixed

How to test:

• Run all unit tests, should all pass
• Test the above Keybindings.json
• Single modifier press should not activate chord (check notification bar bottom left no changes)
• Shift+Alphanumeric should work as usual
• Shift, Shift+Alphanumeric should work as usual no matter how quickly Shift, Shift is pressed (because of keyUp only detection)

Performance Test:

• Hold backspace on a large string; should be no lag
• Type fast; should be no lag

I'm finding my self pressing "Shift Shift" in VSCode release when cross referencing code for this PR 😂😂😂🤦‍♂️

[ghost]

All CLA requirements met.

[alexdima]

Thank you!

[andersonpem]

Wow! Finally! Thanks guys!

[istvandesign]

This is life changing! VSCode will be 10x better now ❤🥳 Thanks!