[GL] Map rendering bug omnibus

[bkoropoff]

• [ ] Requiem MAP13 (some combination of map hole and missing bleeds)
• [ ] Doom II MAP21 (mapper goof)
• [ ] Eternal MAP28 (map hole)
• [ ] BTSX E2 MAP09 (bounding box culling issue?)
• [ ] BTSX E1 MAP01 (missing bleed)
• [ ] KDiKDiZD MAP15 (missing bleeds)
• [ ] SID MAP01 (missing flat bleeds, bad stencil wall bleed)
• [ ] Scythe MAP30 (map hole)
• [x] CChest2 MAP05 (bad stencil wall bleed)
• [ ] Scythe 2 MAP23 (map hole)
• [ ] Grove MAP01 (sky rendering/occlusion)
• [ ] HR2Final MAP01 (missing unintentional bleed)
• [ ] AV MAP01 (missing bleed)
• [ ] SKLHALL2 (map hole)
• [ ] Judgment MAP26 (???)