Rewrote the functor cache compilation code

Part of set of MR LHCb!5286 (merged) !4549 (merged) Moore!5206 (merged) DaVinci!1328 (merged)

Main improvements are :

• precompilation of headers in Rec
• systematic usage of these precompiled headers in all projects (cache AND JIT builds)
• same code is used to build caches and JIT libraries
• simplificaiton of the cache code (dropped a lot of python helpers in particular)
• all code is in Rec, nothing is left in LHCb
• mentions to LoKi have (almost) disappeared