Accept `types.ModuleType` as a distribution identifier

I have recently ran into the issue where the importable module did not come from the distribution metadata found by importlib.metadata. This was because the distribution modules were shadowed in sys.path, which can happen often in test environments.

It would be nice if we could pass a module to importlib.metadata.distribution(), and have it find the distribution where that module originates from, if any.

从 importlib.metadata.distribution() 入口点开始，检查 distribution 标识符的解析方式，重点关注 types.ModuleType 以及 sys.path 中被遮蔽的模块。确定传入模块时应如何查找其来源 distribution，包括不存在 distribution 的情况。当模块可以作为标识符被接受，并且针对被遮蔽模块的行为已由测试覆盖时，即视为完成。