Better camera alignment to 3DGS

[hbb1]

1. Support general camera (align to 3DGS camera). Change not to this repo but to the rasterizer Better camera alignment to 3DGS diff-surfel-rasterization#6
2. Support precomp transformation (but normal rendering is disabled)
3. Better description for the usage of unbounded mesh extraction.

[hbb1]

Experiments on DTU

Make sure that the rewritten rasterizer don't affect the reproduced performance. Note that we do not modify the training and testing code.

scan id	d2s	s2d	mean
24	0.466	0.495	0.481
37	1.057	0.748	0.903
40	0.395	0.399	0.397
55	0.492	0.482	0.487
63	1.120	0.764	0.942
65	0.943	0.955	0.949
69	0.767	0.825	0.796
83	0.954	1.692	1.323
97	1.127	1.379	1.253
105	0.625	0.844	0.734
106	0.524	0.904	0.714
110	1.405	1.142	1.274
114	0.348	0.445	0.397
118	0.617	0.835	0.726
122	0.455	0.555	0.505
Mean	0.752	0.830	0.791

[hbb1]

I think it is ready to merge the updates into the main branch.