Add missing navigation node icons

Co-Authored-by: Michael Alexsander <michaelalexsander@protonmail.com>

editor/icons/icon_navigation_agent.svg

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+<svg clip-rule="evenodd" fill-rule="evenodd" stroke-linejoin="round" stroke-miterlimit="2" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg"><g fill-rule="nonzero"><path d="m9 1c-1.371 0-2.308.429-2.939 1.074-.668.663-1.34 1.324-2.01 1.985-.046 1.741.757 4.327 2.365 4.843.178.317.384.649.584.977v5.121l2-2c2-3 4-6 4-8s-1-4-4-4z" fill="#fff" fill-opacity=".39"/><path d="m7 3c-3 0-4 2-4 4s2 5 4 8c2-3 4-6 4-8s-1-4-4-4zm0 2c1.097 0 2 .903 2 2s-.903 2-2 2-2-.903-2-2 .903-2 2-2z" fill="#e0e0e0"/></g></svg>

editor/icons/icon_navigation_agent_2d.svg

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+<svg clip-rule="evenodd" fill-rule="evenodd" stroke-linejoin="round" stroke-miterlimit="2" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg"><path d="m8 1c-3 0-5 2-5 5s3 6 5 9c2-3 5.007-6.03 5-9 0-3-2-5-5-5zm0 2.5c1.371 0 2.5 1.129 2.5 2.5s-1.129 2.5-2.5 2.5-2.5-1.129-2.5-2.5 1.129-2.5 2.5-2.5z" fill="#e0e0e0" fill-rule="nonzero"/></svg>

editor/icons/icon_navigation_obstacle.svg

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+<svg clip-rule="evenodd" fill-rule="evenodd" stroke-linejoin="round" stroke-miterlimit="2" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg"><g fill-rule="nonzero"><path d="m4.607 8.379c-1.798.928-3.607 2.072-3.607 2.621 0 1 6 4 7 4s7-3 7-4c0-.549-1.809-1.693-3.607-2.621l.607 1.621c2 4-10 4-8 0z" fill="#fff" fill-opacity=".39"/><path d="m8 .875c-.375 0-.75.375-1 1.125l-3 8c-2 4 10 4 8 0l-3-8c-.25-.75-.625-1.125-1-1.125zm-1.5 4.125c1 .5 2 .5 3 0l1 3.5c-1.5 1-3.5 1-5 0z" fill="#e0e0e0"/></g></svg>

editor/icons/icon_navigation_obstacle_2d.svg

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+<svg clip-rule="evenodd" fill-rule="evenodd" stroke-linejoin="round" stroke-miterlimit="2" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg"><path d="m8 .875c-.625 0-1.25.375-1.5 1.125l-3 10h9l-3-10c-.25-.75-.875-1.125-1.5-1.125zm-1.5 4.125h3l1 4h-5zm-4.5 8c-1 0-1 2 0 2h12c1 0 1-2 0-2z" fill="#e0e0e0" fill-rule="nonzero"/></svg>