Commits on Aug 30, 2022

1. inference: revive CachedMethodTable mechanism …

   `CachedMethodTable` was removed within #44240 as we couldn't confirm any
   performance improvement then. However it turns out the optimization was
   critical in some real world cases (e.g. #46492), so this commit revives
   the mechanism with the following tweaks that should make it more effective:
   - create method table cache per inference (rather than per local
     inference on a function call as on the previous implementation)
   - only use cache mechanism for abstract types (since we already cache
     lookup result at the next level as for concrete types)
   
   As a result, the following snippet reported at #46492 recovers the
   compilation performance:
   ```julia
   using ControlSystems
   a_2 = [-5 -3; 2 -9]
   C_212 = ss(a_2, [1; 2], [1 0; 0 1], [0; 0])
   @time norm(C_212)
   ```
   
   > on master
   ```
   julia> @time norm(C_212)
   364.489044 seconds (724.44 M allocations: 92.524 GiB, 6.01% gc time, 100.00% compilation time)
   0.5345224838248489
   ```
   
   > on this commit
   ```
   julia> @time norm(C_212)
    26.539016 seconds (62.09 M allocations: 5.537 GiB, 5.55% gc time, 100.00% compilation time)
   0.5345224838248489
   ```

   

   aviatesk committed Aug 30, 2022
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