Add a new method to check if Thing has a parent

[ramon-bernardo]

Pull Request Prelude

• I have followed proper The Forgotten Server code styling.
• I have read and understood the contribution guidelines before making this PR.
• I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

Introduces a new method to the Thing class that allows checking if a Thing instance has a parent. This providing a direct way to determine parent-child relationships, in addition to the existing if (getParent()) {}.

Before

Tile* tile = nullptr;
if (!parent->getParent()) {
    tile = parent->getTile();
}

After

Tile* tile = nullptr;
if (!parent->hasParent()) {
    tile = parent->getTile();
}

New Lua method

local container = Container()
if container:hasParent() then
    ...
end

[Shawak]

Returns whether or not this node has a parent.