[4.2] Missing description for combination J+M

[Kostelano]

Pull Request for Issue #38163.

Summary of Changes

Added a description of the J M Toggle Menu combination to the new plugin System - Keyboard Shortcuts.

[Quy]

I have tested this item ✅ successfully on e7cb3f1

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[viocassel]

I have tested this item ✅ successfully on e7cb3f1

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/38165.}

[Quy]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/38165.}

[roland-d]

Thank you.