<p>Given the coordinates of two <strong>rectilinear</strong> rectangles in a 2D plane, return <em>the total area covered by the two rectangles</em>.</p>
<p>The first rectangle is defined by its <strong>bottom-left</strong> corner <code>(ax1, ay1)</code> and its <strong>top-right</strong> corner <code>(ax2, ay2)</code>.</p>
<p>The second rectangle is defined by its <strong>bottom-left</strong> corner <code>(bx1, by1)</code> and its <strong>top-right</strong> corner <code>(bx2, by2)</code>.</p>