feat: Enhance keyboard shortcuts for better cross-platform support

[boomzero]

What does this PR aim to accomplish?:

This pull request updates keyboard shortcut handling in the XMOJ.user.js script to support both Ctrl and Meta keys for triggering specific actions, improving compatibility across different operating systems.

How does this PR accomplish the above?:

• Updated the keydown event listener in the DOMContentLoaded handler to trigger the AutoCheatButton click when either Ctrl+Enter or Meta+Enter is pressed.
• Modified the keydown event listener in int main() to allow SubmitElement to be clicked with either Ctrl+Enter or Meta+Enter. [1] [2]
• Adjusted the keydown event listener for the ContentEditor to trigger the OKButton click on either Ctrl+Enter or Meta+Enter.

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