Reorganzie a few things in object.d so similar constructs are found next to each other

[JinShil]

Followup to #2647, #2644, #2643, #2634, #2763, #2765, #2766, #2769, #2772 , #2774, #2775

This is a continuation of work to clean up object.d.

Also, this makes the Object class dominate nearer to the top of the file. This is object.d afterall.

[dlang-bot]

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