Split up `renderlights.cpp`

[no-lex]

The general g-buffer and lights rendering file renderlights is very long (5100 lines) and is not particularly atomic; functionality covered in this file includes:

• ~~screenspace ambient occlusion~~ https://github.com/project-imprimis/libprimis/commit/a5edbdfb0b7ec6baac1380bb61a0c110309fa427
• multisample antialiasing
• g-buffer setup and rendering
• shadow map setup and rendering
• ~~cascaded shadow maps~~ https://github.com/project-imprimis/libprimis/commit/cd859b66af2b819dfc36d9a86c0853bf3c5c4a85
• light entity metadata
• volumetric lighting
• reflective shadow map calculation (rsm)
• ~~hdr and bloom~~ https://github.com/project-imprimis/libprimis/commit/e4f4a81960cda5f84c0c81d3b15e5614e9e17291

As many of these individual topics should be covered in their own file where they can be coherent and contained.