Off hand improvement (Java) Quality of Life [Shield + Spear fix]

Add a key that, when combined with the left or right click, performs the action of that click on the off-hand.
Some examples:
I have a pickaxe in the off-hand, and i want to mine with it, i do ALT + Left-Click then i use the off-hand to mine blocks.
IMPORTANT EXAMPLE: If i have the spear, and a shield, when i do ALT + Right-Click, then it will use the Shield instead of the spear.