Move more files away from OpenRA.Mods.RA

Basically what's in this PR:
 - Moved several traits from Mods.RA to Mods.Common
 - Moved several render traits from Mods.RA to Mods.TS
 - Made TD and TS namespaces consistent with what was decided in #7036
 - Moved the Drag activity from Mods.RA to Mods.Common